may be you are looking for following

'Get the difference in minutes
vMinutes=((hour("02:00 PM")-hour("12:10 PM"))*60) + (minute("02:00 PM")-minute("12:10 PM"))
'get the hour and minutes and convert to time
vTime=cdate(cstr(int(vMinutes/60)) + ":" + cstr(vMinutes mod 60)) 

that will return 1:50:00 AM
you can make a function timeDiff that will take value of your parameters