with answer cell formatted general

you could use the int function
with
a1 12/1/04 12:20
b1 1/4/05 13:10
formula
=int((b1-a1)*24)
would give you 816 (hours)

if you needed more accuracy you could use
=((b1-a1)*1440)/60
which gives 816.8333

plain =b1-a1
gives a result of 34.03472222 (days)

A