As a rule of thumb, I do not stop on any ride that is less than 60 km. From 60 km and up (usually I either do 50-60 or 70-80 as regular rides) I sometimes plan a stop.

mostly that is because the rides that are <60 km are in the morning before, or in the evening after work. Or when I do a ride but do have to be home soon. So there is a time contraint there. The rides that are longer are usually in weekends and when I am free. On those rides, there is not sense of urgency and if I know a nice spot on the route, I stop there to relax. Those rides, to me, are not just training but also just for fun, so I would take a break even if I dont need it. Of course on the bike, I do have my usual pace.