@ OP, after years of playing 4e, here are my thoughts on turn time:
Familiarity with classes is a big one, and of course, that class' own complexity. I expect a Wizard to take longer than a Slayer for example.
Forced choice has generally been my biggest problem, which has led to my primary 4e houserule: You may use a single encounter/daily up to the maximum number of times of that type or greater of daily that you have for your level. ie: if you have 4 "standard" encounters and 2 minor encounters, you can use one standard 4 times, or 1 minor 6 times. This both increases and reduced player choice, allowing players to use the abilities they enjoy and understand over potentially boring, useless or confusing abilities instead. I find that it's a lot easier to decide what to do when you can just choose the power you like and know over the power you don't like and don't know.
Finally: I would ask, how many players do you have?
I generally estimate about 1 minute per player, so with your average group, a round should be about 5 minutes. The DM should have a good idea of what they want to do before the players are done to keep things moving smoothly.