The time for example if you are using the collection skill on a mob.
You see the button that is needed until its finished, after that the next mob will be choosen and your char attacks them

Or can you kill a mob at your lvl with 1 hit ? NO, so you can set the time until the mob is down to attack the next one.
Its a good idea with the time I used them for collection and killing mobs so it needs longer

Remember not all mobs respawn fast too.