One of my fave afternoon training runs is round the Birmingham Outer Circle bus route. From home-town and once round its 50km.
The bus timetable is 2:30. I get it done in 2:15ish.
Don't bother with stopping for coffee, it not long enough.
Now DIY by GPS is available, two laps ( one in each direction ) is a 100km BP. About five hours on Friday afternoons.
Don't get too uptight about riding round in circles all day. The MidMesh Stratford-Measham-Alcester-Stratford triangle is 155 km. Two of these is 310km.. Home is on one of the strings, so a stop-off for coffee and nosh is en-route.
This is, to my understanding, why the MidMesh was created. Take for example Stratford-Evesham- Alcester-Stratford, 55km on paper, 51km in reality. Ride round this triangle ad nauseum watching the Damsons ripen.