Is there a way to show a field with a calcuation that shows time elapsed based on two fields?

For example there is a "Start Time" field and "End Time" field (so say "1200" to "1315" military time) and the calcuation field would show "1:15" for the time elapsed.

Hope that makes sense and THANK YOU in advance for anyone who knows how to make this calculation!

If they are time fields, you can simply take the difference:

End Time - Start Time

... except of course when the end date is past minight, in which case you'll end up with a negative result.

To solve this you need to take the start Date and End Date into account.

End Time - Start Time + ( End Date - Start Date ) * 3600 * 24

The "3600 * 24" is there because time is measured in seconds, while dates are measured in in days. There are 3600 * 24 seconds in a day.