The hotel will have a posted bus schedule. You don't actually wait for a tram- it's a real bus. WDW is HUGE!
If you know where you're planning to stay, just contact the hotel and ask for their schedule. Then you'll know how to plan your days. If you have a rental car, then you have that much more flexibility.
Don't expect to get onto the Disney bus system from Downtown Disney - they only run bus service to/ from Disney resorts.