If we were so programmed like robots, it would be easy to answer this question. But since we all are as alike as chalk and cheese, there is no one set rule for the amount of sleep that is necessary for you. Research shows that anywhere from 4-8 hours are good so some can survive with even 4 hours and some don't even feel rested with 8. It depends on how tired you get, the kind of work you do, how much sleep deprivation you have had, the quality of your sleep different types of activities and so many other factors.
Find out what is your optimum best under which you function the best. Then also take into consideration what you have been doing and how you feel when you wake up in the morning. If you feel groggy then you might do with some more and sleeping in the bus to recuperate is not at all a bad idea. Keep in mind that highly emotional episodes can tire you just as travelling through time zones. So if you do OK with say 5-7 hours, then that it is OK for you and you could probably split it like you have already.