substrac datetime

Question

hi
i need to calculate different between DateTime
i have 2 param for start date and end date
for example 2013/01/01 10:30   &   2013/01/03 17:00
 
and i need thet return count hourse between 07 util 15  and from 15 util 19 and from 19 util 07

please help me how to solve it
thanks