Hours, with more to go.
The dirt came off easy enough, but there's acid rain damage to the paint and windows too. I used an orbital polisher and got the paint (need to do the roof one more pass), but I've yet to get the glass clean, NOTHING takes those spots off. Paint thinner, alcohol, vinegar, steel wool & comet, carb cleaner, oven cleaner...no effect.
I'm still trying to figure that problem out. The paint took about 4 hours of using a polishing compound, then waxing the entire car afterwards, but it was worth it!