NO
If they're both on the same date, then they mark a period of 21/2 hours.
31 and 1/2 hours
2 hours.
21 hours
9 hours, 45 minutes
61/2 + 24n hours where n is an integer.
7:45 am to 6:15 pm is 10 hours 15 minutes (101/4 hours)
10 hrs
There are 35 minutes
NO
If they're both on the same date, then they mark a period of 21/2 hours.
31 and 1/2 hours
7:45am to 12:15pm = 4.5 hours (4 hours 30 minutes)
31 and 1/2 hours
Within any time zone, 6:45 AM to 7:45 PM of the same day is 13 hours.
Four pm means 4 o'clock in the afternoon. 10:15 pm means a quarter past ten in the evening. So, there are 6 hours and 15 minutes in between.