How long it takes to complete, or how many levels? Well, RPG's don't really have levels so count Saga out The only Panzer I've played is the first one and, I passed it (yippie!) - from my memory, I think it has 10 levels It would take an hour and a half to complete if you continued about 5 times (as I did)
PD would be about 1,5 hour (easy mode -not all levels) or 2-3 hours (normal, hard)
PD Zwei is about 2-4 hours, but is more fun to play again since you can take different paths through the levels. Also, Zwei has loads of secrets that you can find by playing (pandoras box). I recommend getting all of them anyway, even if they are easy to complete, since they are all fantastic games.