Rides for overweight unfit people?

Whilst I agree to a certain extent with the comments on attempting longer rides I honestly don't believe they will work for everybody.

Of course. My point was that they do seem to work for a surprising number of people about whom you'd never have thought it.

I was backstop on a club ride recently with a mixed ability bunch of mostly social riders. We covered some 40 miles and for the last 10 I ended up nurse maiding a rider at a pace not much above walking. I doubt that rider would get anywhere near completing a ride such as Dunwich although I too have been amazed at some of the riders and their bikes that turn up and complete similar events.

Yes, one of the keys is that there's no time limit--I've seen people take up to 16 hours. What makes bike riding hard is competing against others. :)

The big danger of attempting too much too early is failing and losing interest when with a little and often approach, huge improvements could be made.
True, of course. It depends on what works for each person.