From what I remember, flight hours do not expire, BUT, golden rule - your instructor will only signal you ready for exam, if she/he is sure you will survive the 100h after license issued. If you are a smart shot, you may not need the 45h on instruction, but they won't be a problem either. If you try to fool and take a shortcut, because you won't be able to fly sufficient for 45h, you most probably kill your family on one of the first flights. Do your flight instruction hours, until ready to pass exam and I bet, after such long time it'll be more than 45h.