24hr Time Calculations

[syzygetic]

Anybody have a good program for calculating the elapsed time between two times? As an example, in HHMMSS format,

090000
to
163200
is
7h32m

My particular use case is on a DM42, so any HP42 program should work fine, but I can't seem to find one out there. My intent is to take the program and integrate the sum feature, so I can add the resultant elapsed times to those registers and use the stats features on them.