Randomly selecting a time on the half hour with a one hour buffer between two columns

I have a dataframe containing two different columns:

StartTime	EndTime
8:00	2:00
8:00	12:00
8:00	4:00
2:00	6:00
12:00	6:00

I want to create another column "SelectedTime" that is a randomly selected time on half hour increments (1:00, 1:30, 2:00, 2:30) with an hour buffer between StartTime and EndTime. So for row one it would be a random time between 9:00 and 1:00. Is this possible?