If the two times are in one day, the easiest way to work out the difference is to do the calculation in easy chunks.
3:25 to 11:25 is exactly 8 hours. From 11.25 to 11:46 is 21 minutes, so the total difference is 8 hours 21 minutes.
If the times are in different days, the chunks are different. 11:46 till 12 noon is 14 minutes. From noon till midnight is 12 hours, and from midnight to 3:25 is 3 hours 25 minutes. Add the minutes together=39 minutes. Add in the 12+3 hours=15 hours and 39 minutes.