How long did it take you to rebuild your

I agree with @ESP47 when he says it is easy and not to farm the job out. I have done several heater/AC boxes, and they are easy. That being said, I have never been able to do one in 4-5 bours, but I have always done a complete restoration on them, and there was usually some damage. Like @Professor Fate said, it depends on a lot of factors. You said you wanted to "rebuild" it. If that just means take it apart, clean it up a bit, put in a new heater core and a few seals and then put it back together, 4-5 hours is possible. If there is damage, of if you want to paint it and restore it to look like new, I think it will take more than 4-5 hours.