I agree with hardening them off a bit. That's a pretty drastic change. Although I raise chicks outside from day one even in the teens and twenties, they haven't been in the house for a couple of weeks first - they are out immediately after a 24 hour observation period for shipping stress. When they go out, the pad is at 6 at first.
As far as when to turn the heat down on your heating pad, that depends entirely on the chicks. There are no really hard and fast timelines with MHP - the chicks will let you know if they're too cold and they'll let you know when you can turn it down. I imagine at 2 weeks old they are still sleeping under it at night, or at least on top of it. I know that in the beginning, especially the first time folks use this, they look for a timetable on managing the heat, like they've learned from heat lamps - 95 the first week, 90 the second, etc. That doesn't apply with MHP. So I'd leave your pad at 4, with the chicks in a cooler room, and watch them, adjusting as necessary.
Not the cut-and-dried answer you were looking for, I know, but this system is based on what the chicks need rather than a rigid formula.