I'd put them and the pad out, but then I'm kinda gutsy that way. Set up MHP, turn the heat up a notch, and then watch them off and on through the day. You'll probably find that they are terrified at first and will huddle together for security, then start exploring almost non-stop. If they are adapting well, I'd leave them with the pad up for the first night, then drop it back down the second day and leave it there for a day or so. Mine are outside and the pad is on the lowest or second lowest setting by this age, and off all heat by the end of the 4th week.
NOTE: I am NOT familiar with using pads that have "low, med, hi" settings. I can fine tune mine a little better, having settings 1-6. So if I'm off base here, will someone with a pad that has the same settings as
@BBZZZZTT has chime in? I don't want to give bad advice.