I think DATEDIFF would be your best option. I know you are looking for the difference in time within the same day, but couldn’t you just pass DATEDIFF two DateTime types with the same date, but different times?
// Should return 300
DATEDIFF(mi, '2015-02-19 08:00:00', '2015-02-19 13:00:00')
2
solved How do I get the minute difference between 2 times in T SQL?