remember that a date is stored as a number, so to take 1 day off (24h) it is just date_-1. Look at this:
dummy_=#02/01/2008 10:00:00#
? Format((dummy_),"dd/mm/yyyy hh:mm:ss")
02/01/2008 10:00:00
dummy_=dummy_-1
? Format((dummy_),"dd/mm/yyyy hh:mm:ss")
01/01/2008 10:00:00