Everyone has his or her own pace and it's highly dependent on the opponent and the general approach to the game.
I say that anything between 15min and 2.5hrs is plausible.
If you are organized, you can cut the playing time considerably.
My experience (I play PBEM only):
-JAP Scen01 before June '42 takes roughly 1hr per turn
-JAP Scen01 between June '42 and the end of '43 takes roughly 30min per turn (exceptional situations excluded)
-ALL Scen01 before mid '43 takes 1hr per turn
-ALL Scen01 after mid '43 takes between 1hr and 2hr per turn
These are averages, obviously.
Individually, I have a time allotment of 1hr per turn. Most of my games have a very precise and clearly defined planning and this really cuts the time devoted to each turn.
When you are in the initial Japanese expansion, for example, having a GANTT with the various units and their activities helps a lot.
A very rough initial "feasability study" I did recently for my last PBEM:
