Question: how to calculate difference between two dates and time?
Answer: Type two full dates and times. In one cell, type a full start date/time. ... 
Set the 3/14/12 1:30 PM format. Select both cells, and then press CTRL + 1 (or. ... 
Subtract the two. In another cell, subtract the start date/time from the end date/time. ... 
Set the [h]:mm format.