Maybe not the fastest however all that material has be brought up onto the roof and the old stuff ripped up and carted away. 30 hours is ~3 man days. A 3 man crew doing that in a day doesn't really sound too bad to me.

One guy doing it himself in 3 days sounds ok, too.

Just my 0.02.

"He said it takes about an hour to replace a 4 by 8 sheet - that seems like way too much time on a simple moderately sloped roof"

Sounds about right.

You have to remove the old deck, clean up any old fasteners that will be in the way of the new sheet in the rafters, buy the sheets, deliver the sheets, get them on the roof, remove the debris form the roof, load the debris, dispose of the debris, fasten the new sheet (and maybe trim it some to fit).

that is a serious repair and his labor charge sounds about right

I agree - unless a crane dropped all 30 sheets, and the shingles off on the roof, and then held the dumpster right at the lip so cleanup was a breeze?

seriously - you get one sheet of plywood, one roll of paper, and three packs of shingles up that roof your own self, and see how long it takes.