I'm fairly certain that they were talking about asynchronous updaters for the values, and not sleeping in onPaint.
Doing so could be mildly beneficial, using something like a Scheduler or ScheduledExecutorService, altho as Swizz mentioned, it's not really necessary.
If you did infact talk about adding sleeps in onPaint, tho, then... well.. don't. Threads that hande graphics/rendering should never be obstructed from returning, as it can make the entire user interface unresponsive. Especially if it's the EDT being sent to the paint methods.