I'm away from my main PC and don't have Access on this machine, so can't knock out the exact answer, but I'd have a utility table set up with a single record (I use one to enter all corporate ID data, like phone numbers, address etc) with a field for the date.
Check the current date against this value, and if they are the same, do nothing. If they are different, increment your value by one, and write the new value to the table.
Hope this helps.
The Missinglinq
"It's got to be the going,
not the getting there that's good!"
-Harry Chapin