During that transition period you do not have to use Colemak exclusively. You're practicing a new motor skill, and the returns on such practice diminish rapidly after an hour or so per day.
Once you've learned Colemak, you will have to use QWERTY for just a short time each day to make sure you keep those neural pathways from decaying. I did not do this, and I regret it. I do alright on a QWERTY keyboard though; it just slows me down a bit. On a mobile device, it really doesn't make any difference, since the letters are in front of my eyes.