Hi, Ian.
Who cares what the actual transfer date was?
No, I don't mean that as a smart-aleck question. I mean: To whom is this date important? Bank A doesn't care what you put into Quicken; it keeps its own records. Bank B doesn't care; its records are correct. The only person who cares is you.
Why do you care? Are you preparing a financial report as of a particular date during the transfer "limbo" period? Is an investor or lender or other interested party looking over your shoulder or at the report?
In the olden days, before there were electronic transfers, you might write a check on January 30 and mail it to your creditor on January 31. The payee might receive it on February 3 and deposit in his bank on February 4. By February 6 it might have made its way back to your bank, where it would "clear" and be marked "cancelled". Which of those dates would you record in Quicken? Which date would the payee use? How about the two banks?
My point is simply that each party to the transaction should properly record it as of the date that is meaningful to that party.
Since you didn't have to keep the books for Bank A or Bank B or for your creditor, the only date in your checkbook would have been the day you wrote the check and mailed it. If it did not show up on your January 31 bank statement, you would not have added it back to your checkbook balance, but would have listed it as a reconciling item, an "outstanding check". You might have been interested to note the dates stamped on the back of the cancelled check when you got it back, probably with your February bank statement. But you would not have tried to record any of those dates in your check register. The important date for your accounting was the date on which you sent that check.
I would use a similar method to record the transfers you are asking about. The only thing unusual is that you say the receiving bank gets the money before the sending bank sends it. So, for a day or two, you appear to have more money than you really do. But that just means that the transfer-in-transit is a reconciling item. The receiving bank has the money, so its balance is correct. The sending bank's balance is overstated by the in-transit item, which must be subtracted - just like an outstanding check. The sending bank doesn't know about the transfer yet - but you do, so you must show the reconciling item during the transit period.
If it were my books, I would record the transfer - in both bank account registers - on the date that the transfer is ordered, the date on which the transfer begins. From that point forward it is really just like a mailed check. You've set the wheels in motion (or the bank did as your agent) and the rest of the actions are just completing the process you started. Just like when you mail a check.
If you feel you must keep track of the in-transit deposit, then you can use a Suspense account, by whatever name. Andrew suggested "Cash", but I might call it "Transfers in Transit". Because the receiving bank records the transfer first, during the interim, this account would show a credit (liability) balance, which would be deducted from the sending bank balance for reporting purposes. RC