Driving time, if you take the Panamerican highway through the highlands (beautiful scenery), should take you from 3.5 to 4 hours. If you take the "coastal" (via Escuintla), it could take you a little...
Depends on if you are driving or taking a shuttle bus. It takes about 2.5 hours on a shuttle but I think you could drive it in a little less as long as you didn't get lost.
About two and a half hours. You must know that there are a lot of curves and that the time will increase or decrease depending on what type of car you are going in.