It's not really an exact science... more a matter of established history.
If you're trying to be competitive, the studios will probably expect you to run a reasonably comparable schedule to the theatres you're booking against.
On the other hand, a friend of mine has a theatre that's run a single evening show since 1947, with few exceptions. He's booking about 85% first run in his market, and competing against a small twin that runs almost from noon 'til midnight.
Yes, there can be exceptions. In a few cases, that owner had to agree to run two evening shows a day during the first week or two... but it was established that this would not change his expected norm.
As far as I can recall offhand, master licenses don't cover this in any detail, so a theatre can probably do whatever they establish as customary for them unless otherwise negotiated when a film is booked.
[This message has been edited by rodeojack (edited December 09, 2005).]