The day the item was deferred does not count. Let's say your company clock starts at 0300 local.

If you deferred an "A" item at 2300 today, then today is "day zero".

You could then fly from 2300 to 0300 and then continue into tomorrow "day one" and all the way up to 0300 the following day. After 0300 on that day you are in "day two" are are no-go.