The first time I had a rear puncture on my M6L it took me over an hour. I have had 5 or 6 since then (normal green Brompton tyres). Last one was two weeks ago, and I changed the tube by the side of the road. It took 10 minutes. It's all familiarity.
WRT to Marathons, an experienced cyclist friend at work fitted them. It took him 2 hours to get the damn things on the rims.