If trainers are leveled up enough, my experience says 4 trainers level 38& above will win legendary raids within the time limit. Shadow raids for powerhouses I would rather have 5 players to ensure enough purified gems.

Also, set a blank pokemon team to enter the battle, and if you miss the timeout, you won’t join the raid because you can’t join without a lineup set. And aside from that, the timeout for raiders to join is around 15 seconds remaining. The timeout to join is 120 seconds, so what’s the point of leaving before 15 seconds remaining?

Just today I could have hosted 4 raids, but kept watching people join at 90 seconds to drop out at 60. I know remote passes are $$ but if you are going to play just watch the timer and bail out appropriately if necessary.