I don't think there is anything in the text about Dominic's intentions, aside from the fact that he wants to entice at least one of the girls into working on his time machine forever and ever - but it's not even clear why he wants to do that. Then again, I guess the Devil doesn't need a reason to tempt people.

I'm still not sure what the point of the spell was, thematically speaking. It seems very odd that he would put a spell on his daughters, but not interfere when the Devil himself tried to victimize them. Maybe the point is that parents can't protect their children from everything - that girls need to learn how to protect themselves?