You should expect your transfer coach to arrive at the pick-up point a few minutes before the loading time.
If you are early, then this may not yet have arrived and you are asked to wait elsewhere until it does arrive. The app will give more detailed instructions.
The driver will most likely stay with the vehicle so you should look for instructions from the reps/staff in the airport for when you should head towards your transfer loading point, or look out for an in-app message to let you know it is ready for you to board.