Sorry i am a little tired of reading all those speculation about karma and scav raidtimes,waiting times + these complains that you always join late … etc. Maybe i can help with some confusions
PMCs are starting raid instances on the server by joining a game.
After the game has started, there is an instance of the map for x amount of players, which are all pmcs at start, when available.
Now whenever a player dies(regardless if its a pmc or later a scav), a slot is open for a scav to join and the next scav in the matching phase will be picked and thrown into the map. (totally rng if the next death is on a instance that has 20 min left or only 10 min)
That why on interchange it is more commen to join in early (killa rushing and dead pmcs in the first 5 min)
And on reserve you have these long waiting times because lots of scavs want to join but there are not enough slots for them. So they have to wait. (every other map has matching times under 2 min)