Note From Jim: Wednesdays.
All Wednesdays are banking "Settlement Dates" around the world. The first Wednesday of each month is even more stringent. The dates are when, by close of business, all accounts between banks must be reconciled and no one can be overdrawn. Its purpose is to squeeze out any bank that is insolvent.
If I am guessing right, by Friday there may be funeral wagons in front of some major banks.