I have only recently started reading this Board and a few others here in Fooldom. I plan on using Foolish investing methods in my post retirement IRA and have a question which may be more accounting than investing but...

What point in time does one use for valuing an IRA acct when starting Substantially Equal Periodic Payments?
The 1st of the month the withdraws start?

Note: I must use the SEPP method to avoid penalties, retired under 55.

Thanks for any guidance.
JoeW3