Well, to me "rebuild" isn't synonomous with "Cup winner". A rebuild is going to turn a non-playoff team into a contender, and whether that contender actually wins a Cup depends on other factors. For all we know, Regier could make all the right moves, all the prospects could turn out great and the team will still never win a Cup because of (fill in the blank).
So to be back in the playoffs with a team that should be able to win a round or two shouldn't take five years. To have a Cup winner depends on other things (Grigorenko explodes, Kane signs as UFA, other UFA signings, etc). One shouldn't take five years, the other could take forever or never happen no matter what.