However the particles fade in! everything I do - it won't just start with the particles on screen. They always fade in. Here are my settings here focused on the opacity map, but not matter what they still fade in!:
When you slide the layer ahead in time is there still some of it after frame zero? A better solution is to make your timeline longer and slide your clip down in time and leave the particles to start generating on nothing before the clip but render the whole thing and just edit the first part out.
I haven't used CC for a long time as I use Particular now - is there no "pre roll" setting? where you can set how many frames to start the effect before frame 0?