Whatever you feel like, it's not a race after all. I don't count total time, only moving time, but on a century I'll only stop long enough to pick up food, throw banana peels and what not in the garbage and use the portaloo if needed. Usually I'll stop around 40 miles then 70 miles. If you are taking the p!ss and taking 20 minutes a time for every stop then moving time and total time will be pretty far apart and your 6 hour time is probably more like 8.