Hi, I don't have answers to all the questions below but I'll try my best to answer some of them.
I think this depends on the car. Different car models have batteries of different capacities, the alternators are different so I don't think you can estimate a value for that. My Mazda BHALP charges it's battery within 30 mins and I can see a reasonable battery voltage after that.
Well, In cars we have lead acid batteries. The gravity (The specific gravity in more accurate terms) of the acid gets changed while charging and discharging.
As this diagram shows the specific gravity and the cell voltage gets down when the battery is getting discharged. When it is charged the gravity gets increased again.
Generally the batteries are charged using a little higher voltage than the battery voltage. The theoretical potential difference of a battery cell is 2.2V and you have 6 cells in your battery so the ideal potential difference might be 13.2 though it is marked as 12V. So generally alternators generate voltages between 14.2 V to 14.5 V. When you charge the battery the potential difference (the actual voltage you observe between nodes) get decreased. That is the reason that we do not recommend to remove the battery terminal when the engine is running. It can ruin your electronic systems, bulbs etc.
Theoretically yes. But I don't have an idea of the length of time. Just use a voltmeter and check battery voltage time to time.