It does help longer when you can do it more. A normal day for me is two hours, with one of those being yoga at the end. Sometimes I'll get five hours in and split it up into two, with yoga practices at the end of each trip. Those are my two-a-days T-days, Tuesday and Thursday.
Yoga really is something I recommend, if you're capable. Even if you can't touch your toes, and a lot of the time I can't, it still feels really good.