Just took the train from the Tambo to AC last week. We were inside MP at 10:15.

The timing of your trip might matter too- we didn't have a line or wait for a bus. From what I've heard, there can be a queue depending on tim of year. If its this summer, you might expect as much.

Cusco is pretty cool. Definitely worth more than a day, especially to see the ruins nearby. Why not stay at the Palacio? Quite nice hotel. My gold got us an upgrade to a junior suite. Directly across from Qorikancha.