sed doesn't really have comparisons, variables, expressions, or even numbers... It doesn't have anything you're asking it to do. You'd have to tell sed how to comprehend numbers in the form of many big and ugly regular expressions like /0[0-2]:[0-9][0-9]:[0-9][0-9]/ one per range.

Or you can just use awk, which actually has numbers, variables, expressions, and comparisons, and use these numbers, variables, expressions, and comparisons to solve it in one operation instead of 8 plus further processing.

If the number of lines is intimidating, I bet I can simplify it further given certain assumptions, like column 1 never containing the : character.