AE’s Particle Playground works in a simulated manner and it requires information from a previous frame (other than frame 0) in order to render the next frame. Therefore, if you were to make parameter changes and then park your time indicator at the 5 second mark, AE will have to render all frames previous to the 5 second mark and then render the frame at the 5-second mark.
The general rule is to make changes and then park the time indicator at time zero to view and changes. From there, you might as well perform a RAM preview to view the rendered frames if you’re dealing with a computationally heavy PP comp. For light- weight compositions, you may get by with a little waiting after you park your time line indicator further down the timeline.
It’s also best to create a particle killer property map to kill off old particles. Check old postings for ways to create such a property mapper.
HTH
Roland Kahlenberg
broadcastGEMs
customizable animated backdrops with Adobe After Effects project files