How to know when kitten is bugging older cat too much?

I just adopted an 8 week old kitten today (female, not spayed yet but will be) and I have a one year old spayed female already. They have been playing nonstop since I brought the kitten home, with a rare hiss here or there. The kitten has only hissed once or twice and the older cat hissed a few times when the kitten was chasing her a lot but other than that they seem to be playing together quietly without hissing or fighting. How do I know when they need some time apart or will they figure it out for themselves?