They do. I think the first band performance is @1:15 ish. Someone will correct me if I'm wrong, but I researched this a few months back and adjusted my ADR to see the show.
I thought they started earlier, but the guest relations can give you specific times. Definitely play all day, although I recall a period of about 90 minutes between lunch and dinner, usually they play once an hour.
You can find the most current show information on Steve Soares site Here
He has Biergarten listed as:
Experience the excitement of Oktoberfest with a festive dinner show in the Biergarten.
Daily at 1:15, 2:15, 3:15, 4:45, 5:55, 7:00 & 8:05pm
Length of show: 25 minutes
Seating based on restaurant availability.