Great Guys I never have done it that way. It sounds a little more simple than I do it. :-\
I Use the in game Trigger and the Count down timer of the Max Min Mid.
So if ya start the game in the intel window of the mission editor at 10:00 am and want the the group to go at 11:30 am it would be in minutes 90.
So it would be 90 max 90 min 90 mid. with the appropriate condittions of the trigger for your group.
I like doing it this way. You can have variable times the group leaves the spot.
So it would be 92 max 88 min 90 mid
That way playing the mission doesn't become too predictable.
Just another way to do it.