#1 is OK. (Actually I've always had a slight doubt about whether "different from now" logically makes sense. The earth wan't different from "now", it was different from the way it is now. But everyone, including me, says "different from now", so just ignore that!)
#2 is OK with "days" (not "day").
#3 is not so natural to me. "The old times" is OK in itself, but it doesn't seem t