Changing Time Values In Column

Hello everyone, first time post, I read the rules and I hope this is the appropriate place to post.

I am looking for a way to simply change the values in column B (start time) back by one hour, for instance 06:00:00:00 would become 05:00:00:00. Because this schedule is a broadcast schedule, time is shown in 4 fields hour, minutes, seconds, and frames (hh:mm:ss:ff).
I can't find a way to quickly adjust it, and because my company broadcasts in a lot of different timezones, I spend a lot of time manually adjusting the values myself. It seems frustrating because I know excel recognizes the values, because it is capable of sorting them, of course that may mean absolutely nothing.
I have attached a sample file that I hope should make my problem a little clearer.

Hope my post is ok, Mods please message me if it isn't, and thanks for any help at all, even if it is a simple "this cannot be done"

Thanks!