Just throwing this out there, but I've used Harry's in the past as well. I used RaceChono pro the past two track days and I think it's a big upgrade to Harry's. Much more user friendly, and yes, you can turn it on as soon as you arrive at the track and it will start recording data from your iphone's or external GPS and the OBDII plug. I usually just leave it on until I'm on grid then I just hit record on the app to start the gopro video recording.
I like the GUI which is more modern and readable. The time and speed deltas are also more readable since they are both graphical and numerical. Here's my lap at ACS first time using RaceChrono on a circuit: