Last week or so, I was trying to find the appropriate time for a countdown. I learned through some tests that the countdown is right around -13.96. I believe this might the right one as by the time you control your character the timer will be right around the 0.00 range.

Sorry for the very late response. But for the sake of simplicity the real time count in the rules here starts upon character select (on the frame the selection visual begins), not character control. So no countdown is required. It ends once "FINAL TARGET DESTROYED MISSION COMPLETE" is written on the screen.