Ive got a crf and i change to oil every 10hrs, i brought a hour meter they day i got the bike. Otherwise , if all else fails , just change the oil if you cant remember when you did it last, its not like its an expensive thing to do. and a whole 10mins of your time.
My china motors get oil changes at 7hrs. Dont wanna risk it , they arn't as well built so i keep the on the ball with oil changes on them, and its worked well because ive still got the same motor 2 years later , unlike alot of china owners on this site.