I didn't find an entry regarding this topic yet, so Ima just puts it up here innit.
I set my particles up as snow. Slowly falling down the screen. Romantic. Since whenever I'd enter that scene - it would start at 0 and gradually spawn particles from the top, as if it had just started.
So I added a value to lead time.
But when I enter the scene now, a bunch of snow particles fly in from the left (asif a movie assistant would throw a bucket of them in from the side) following a little pause.. and then snow that started from 0 again.