1996 Buick Regal?

If you have to ask that, then allow for more time...

I had a 1984 Buick skyhawk with the alternator near the top.I changed it out with a rebuilt one in about 50 minutes.The hard part was buying the thing with no car to drive.Alternators are easy as long as you can reach the three pivot bolts,one on each side and sometimes a rear one.The only critical thing is the electrical connection in the back.(A bolt and washer assembly,covered by rubber or plastic.)Good luck.

It is unlikely that the thermostat would cause this problem. A bettter bet would be the heater control valve that switches hot water to the heater core when the switch is set to heat. Inspect the vacuum lines to this swich (on the side of the heater assembly under the dash near the floor board) See if the switch changes position when the controls are changed on the dash. PS The defroster will work with just cool air, or even barely heated air. If it were your thermostat the car would not heat up at all.

It would probably take about twenty or thirty minutes. But if you were in a race against the clock to win the alternator switcherroo championship, I guess you could do it in less than 10.

If you now how it should take 1 hour max.

It depends if you know how to do it.

If you know what your doing no more than 45 mins