I am building a travel form and want the per diem allowances to automatically appear based on the start/end date and time they select.

For example: if they select 8am June 11th as the Start and 6pm June 13th as the end then the number of per diems they receive would be 2 full days. But if they selected 4pm as their return then they would get 1 full day per diem, 1 breakfast and 1 lunch.

Anybody know how I would go about this?