Just FYI you don't have to use pickup mission launch, you can call the roll and still will be in mission.
We have pickup mission setup in our squad that we all join but we roll when our leader says not when the mission says.
So we get loadout information, waypoints and icon color..we get those benefits without using the mission launch.
So if someone DOES change the game clock at the last minute it has zero effect on us.
So that's an option.
Currently I have to guess Frame start on the game clock