The dollar leg keeps banking hours
A stablecoin transfer settles in every hour of the week and the bank leg does not. The gap is carried as inventory, and inventory must sit somewhere signable.
Bits & Blocks||7 min read
Fifty hours in an ordinary week, the token leg of a dollar stablecoin trade settles and the bank leg cannot. The Fedwire Funds Service opens at 21:00 ET on the calendar day preceding each funds-transfer business day and closes at 19:00 ET, Monday to Friday, and it is shut on Federal Reserve holidays.1 Friday 19:00 ET to Sunday 21:00 ET is 50 hours. A transfer of a payment stablecoin on a public chain is indifferent to all of it.
The spread available across that gap is not free money. It is the price of holding an inventory that cannot be squared until the rail reopens, and the position sits with whoever quoted the price.
The window, in hours
| RAIL | WHEN IT IS OPEN | VALUE CEILING PER TRANSFER | WHAT IT SETTLES IN |
|---|---|---|---|
| Fedwire Funds Service | 22 hours a day, Monday to Friday, closed on Federal Reserve holidays1 | No published network ceiling | Central bank money |
| FedNow Service | 24x7x365, with no expectation of planned service downtime2 | 10,000,000 USD for customer credit transfers, since 12 Nov 20253 | Central bank money |
| Circle Mint redemption | Follows the paying rail: same business day for domestic wires received before the daily cut-off, 1 to 3 business days for international wires4 | Set per account by the issuer4 | Commercial bank money |
| Payment stablecoin transfer on a public chain | Continuous | The sender's balance | An issuer liability |
TABLE 1. THE TWO RAILS THAT SETTLE IN CENTRAL BANK MONEY DISAGREE ABOUT WHEN THEY ARE OPEN, AND THE ONE THAT NEVER CLOSES IS THE ONE CARRYING A PUBLISHED CEILING. AT WHOLESALE SIZE THE CEILING IS THE BINDING CONSTRAINT RATHER THAN THE CLOCK.
FedNow is the obvious answer to a closed weekend and it is a partial one. It is an interbank real-time gross settlement service running 24x7x365, settling by entries to Federal Reserve Bank master accounts,2 and since 12 November 2025 its network limit for customer credit transfers has been 10,000,000 USD.3 Two limits survive that. A 60,000,000 USD position becomes six messages, and each message is six separate opportunities for a participant-level control to reject one of them. Separately, service availability is not participant availability: the operating procedures contemplate participant planned downtime, to be scheduled on Sundays between 02:00 and 06:00 ET.2 The rail is open. A given counterparty's bank need not be.
The peg is enforced by the rail that closes
Redemption at par is what holds the price. The GENIUS Act, Public Law 119-27, signed 18 July 2025, defines a payment stablecoin as redeemable for a predetermined fixed amount and requires the issuer to hold at least one dollar of permitted reserves for every dollar issued.5 That right is continuous. Its execution is not, because redemption pays out over a fiat rail, and the fiat rail keeps the hours in Table 1.4
The correction mechanism therefore runs on the bank calendar. When a payment stablecoin trades below par on a Saturday, the trade that would close the gap, buying below par and redeeming at par, cannot complete its second leg until the issuer's settlement bank is able to pay. Anyone quoting into that gap is taking a position for the length of the window rather than for the length of a round trip.
The alternative is to quote only when both legs can settle, which removes the position and the revenue with it. That is the correct choice for a treasury with no mandate to carry inventory, and it should be stated as a decision rather than left as an operational default.
Pre-fund, or lend
Pre-fund both legs before the window opens. The alternative, quoting on Saturday and settling the dollars on Monday, converts a market position into an unsecured credit position with no margin and no ability to liquidate inside the window. A credit position that cannot be closed is worse than an inventory position that can be sized in advance.
Pre-funding costs the return foregone on the idle dollars. At an assumed 4 percent annual opportunity cost, which is an assumption of this note rather than a sourced rate, 50 hours of idle balance costs 0.023 percent of the pre-funded amount, or about 2,283 USD per 10,000,000 USD. That figure is the floor under any spread quoted across the window, before operational cost and before the loss given a mispriced fill. A desk that cannot charge above it should not quote across the window.
The condition that reverses this is a counterparty able to post collateral on-chain that can be liquidated during the window. Collateral that can be seized while the banks are shut turns the credit option from unsecured into secured, and the comparison has to be run again at that point.
The hot balance is set by the window, not by the trading model
Inventory pre-funded for a closed window has to be signable during that window, or it is not inventory. That precondition, rather than the size of the book, is what sets the exposure. A key compromise at 02:00 on a Sunday reaches the entire float the window forced you to hold, because the float has to be there and there is no rail on which to move it away. The same compromise on a Tuesday reaches whatever happens to be hot at that moment, which is a number the treasury controls.
Size the hot balance to expected window flow, hold the remainder behind a threshold policy or a time delay, and accept that an unusually large Saturday order is refused. The alternative, a single hot wallet holding the full book so that no order is ever refused, loses on recoverability: a refused order is recoverable and a signed transfer is not.
This bounds the loss and does not prevent it. A signing service with authority to move the window float can be induced to move the window float, and a threshold policy changes nothing if the compromise sits at the policy layer rather than at the key layer. Ranking that weakness requires naming its precondition, which is write access to the approval rules rather than possession of a key share.
What the expanded operating days change
On 9 October 2025 the Federal Reserve Board announced that the Fedwire Funds Service and the National Settlement Service will operate six days a week, Sunday through Friday, including weekday holidays, with implementation planned for 2028 or 2029 and participation by service participants voluntary.67
Saturday stays closed. Applying the published daily schedule, a Sunday business day opens at 21:00 ET on Saturday, so the closed window would run from 19:00 ET Friday to 21:00 ET Saturday: 26 hours rather than 50. That arithmetic is derived from the operating hours in source 1 and the operating days in source 2, and it should be re-checked against the implementation notice when it is published. Half the carry, the same shape.
Voluntary participation matters more than the headline. If a counterparty's bank chooses not to operate on the new days, the window that binds a given flow is the union of the closures across every institution in the chain rather than the Federal Reserve's own calendar. The next checkable item is the implementation notice for the expanded operating days, published on the Fedwire Funds Service resource page.6
What this does not cover
| NOT COVERED | WHY NOT, AND WHAT WOULD CHANGE IT |
|---|---|
| Correspondent bank internal cut-off times | They are set per institution, fall earlier than the 19:00 ET service close, and are not published in one place. A counterparty supplying its own cut-off schedule in writing would let the window be computed for that flow. |
| Non-dollar windows, including euro, sterling and yen rails | Each operates on its own calendar and the arithmetic above does not carry across. A euro or sterling leg entering the flow would require the same table rebuilt from that operator's published hours. |
| Chain-level finality and reorganisation risk | It is a separate decision from the fiat window and the answer differs by chain. A named chain and a stated confirmation policy would make it a checkable question. |
| The observed size of par deviations across closed windows | This note argues the mechanism and does not measure the magnitude. A dated series of secondary market prices, with venue and timestamp, would settle it. |
| Accounting and tax treatment of the carry | Outside the scope of a settlement note and jurisdiction-specific. A named jurisdiction and an opinion from counsel would change it. |
| Any Bits & Blocks engagement implementing the above | This note describes the mechanism and names no client. Written approval from a client would allow the design and its artefacts to be published. |
TABLE 2. THE EXCLUSIONS ABOVE ARE SCOPE DECISIONS RATHER THAN GAPS DISCOVERED LATE. EACH ONE NAMES THE CONDITION THAT WOULD BRING IT INTO SCOPE.
Sources
Footnotes
-
FEDERAL RESERVE FINANCIAL SERVICES, WHOLESALE SERVICES OPERATING HOURS. frbservices.org
-
FEDERAL RESERVE BANKS, FEDNOW SERVICE OPERATING PROCEDURES, APR 2026. frbservices.org
-
FEDERAL RESERVE FINANCIAL SERVICES, NETWORK LIMIT INCREASE NOTICE, 12 NOV 2025. frbservices.org
-
CIRCLE DEVELOPER DOCUMENTATION, HOW MINTING AND REDEMPTION WORKS. developers.circle.com
-
CONGRESSIONAL RESEARCH SERVICE, STABLECOIN LEGISLATION: AN OVERVIEW OF THE GENIUS ACT OF 2025. congress.gov
-
FEDERAL RESERVE FINANCIAL SERVICES, FED360, 15 OCT 2025. frbservices.org
-
FEDERAL REGISTER, FEDERAL RESERVE ACTION TO EXPAND FEDWIRE FUNDS SERVICE AND NATIONAL SETTLEMENT SERVICE OPERATING HOURS, 17 NOV 2025. federalregister.gov
