On this playthrough I've decided to just wander around Watson a bit before the heist and keep finding streets I've never seen before, even on previous playthroughs where I walked everywhere. This particular street is practically subteranian and its a shame most of the content takes place at surface level or in the main streets when there are great environments like this hidden around the place where most players will never see them.
One person slows down everything or no one slows down at all or just NPCs slow down.
Why did you need that spelled out for you?
Because none of those options would make for an even remotely playable multiplayer experience and I was hoping that there was something else that I was missing.
I have no idea how the mod author is implementing it but a better method would likely be:
Time slow effects all npcs/players/projectiles in a radius with a falloff towards the edge of the radius, time slow can counteract time slow.