I suck - it seems to take me about 40 minutes to fix a flat if I'm patching. If just changing a tube, maybe 25-30 minutes. I always struggle with getting the second bead fully seated, and to a lesser degree prying the tire off. If it's for the rear of my IGH bike, even longer, because it takes more time to get the chain tension just right and get both ends of the axle the same distance back in the dropouts. This is why I put a Marathon Plus on there this spring.

If I was in a hurry, I might be able to do it in 20 minutes.