What is the cut-off time for determining the settlement date of Forex trades?

In a cash account, an investor must pay for the purchase of a security (meaning, the trade must settle) prior to selling that security. If an investor buys a security and then sells that same security without paying for the security in full by settlement date, the investor is considered to be “free riding.” Our implementation of the free riding rule uses an end of day check to see if a position was closed prior to its trade settlement date. Our end of day surveillance would still consider closing a position before settlement a Free Riding violation and automatically puts the account into "Cash Up Front" restriction for the next 90 days…

Spot currency trades executed after 17:00 ET are generally considered the next-day's trades and will be reported on the daily Activity Statement as of the business day following that on which the trade was executed…

You can trade expiring options up to the end of the last trade date if the account has sufficient funds to meet both the real time and projected margin requirements.  The cut-off time for when you can open a new option position that expires the same day or the time you have left to close an open expiring option position depends on the available funds in the account.  Starting 2 1/2 hours before trading ends on the contracts last trade date IB's …

Unless you arrange for a pre-borrow, you will not be subject to stock borrow fees if you open and close the short position within the same trading session. When a short stock position is initiated, a locate is performed so as to make a reasonable determination the shares are available to borrow, however, the actual borrow does not take place until settlement (T+1 for U.S. stocks). If an account closes the short position on the same day opened, the sale and purchase will net and settle on the same settlement date, with no borrowing of shares required…