Counting Days And Hours

I have a questions about counting days and hours.

Imagine that i have an item entering my warehouse on 22/05/2008 at 21h35 and leaving on the 25/05/2008 at 5h42.

A1= 22/05/2008 and B1= 21h35
A2= 25/05/2008 and B2= 5h42

The goal is to count the full 24 hours day and the remaining hours.

For the example given i can say that on day 22 the item only says 2 hours and 25 minutes, on day 23 it stays 24 hours and on day 24 another 24 hours, on day 25 the item leaves at 5h42, so it only stays those 5h42.

So we have 2 full 24 hour days and 2h25 plus the 5h42, the the item were stored 2 days and 8 hours and 7 minutes.

The problem is when the item arrives at (example) 22/05/2008 2h00 and leaves at 25/05/2008 23h00 on another day. Lets say that on the first day the item is 22 hours stored, plus the 2 full 24 hour day and another 23 hours.
So it is 2 days plus the 45 hours, that is 2 days plus 1 day and the remaining 21 hours.

how to add to this 2 full days the 1 day and 21 hours