Well here is one that made us stop and think before answering. We were recently asked what is the longest I should ride in a single day.
There is no specific time for this as everyone is different and it even depends on the motorcycle you are riding. However, it is very much an individual decision.
If you are riding in a group you need to stop based on the rider that is getting tired and needs a break. This could add time to your ride or it could reduce your time based on how often they need to stop. We have been on rides that one rider needed to stop and get off their motorcycle every hour and half or so. They were a new rider and their motorcycle was not set up for comfort. Some people have back or neck issues and need more frequent breaks.
The bottom line is that you are on two wheels and you should never push yourself or a member of your group past what they can comfortably be able to do. Never ride when you are tried or physically trained. Spending more time at stops or even an over night stop if needed is always better than having someone drop their bike or get to where you are going and being so exhausted they can not enjoy the ride or the destination.
Remember for a motorcyclist, riding drowsy and tired is as dangerous as falling asleep while driving. Fatigue impairs the rider and makes them less alert and impacts their ability to control their motorcycle. Know your limit and don’t push it.
If you are a new rider your ride time will improve with riding. If you are an experienced rider then take a look at your equipment and what can be changed or added to allow you to extend your rides without making you tired.