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.
Right now the multiplayer mod being developed will allow server owners to choose how it affects the server. But to answer your question, the mod is being developed more for a GTA RP type server. There will be no "co-op" mode to go through the story.
I'm not following how that solves the "time dilation" problem?
Each server can handle it how they want. Who it affects, etc.
What are the options for handling it
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.