At 11am, 12pm, and 5pm, you can watch the wooden figures dance around on the New Town Hall. My husband's reaction was "Is that it?" It's one of those things you really should see in Munich, but you'll feel as though you could have easily gone without once it's over. More amusing is watching the other tourists gather, and then seeing all the necks craned and cameras pointed in unison.
Marienplatz is a nice place to spend time anyway--plenty of shops, restaurants, architecture to look at--so you may as well plan to be there while the music's going!