>>30039649It can do one or the other since the stat that is boosted/levelling up is determined by what drink you give to the pokemon working in that group. When it's maxed out you can have 3 groups of 6 working on a stat each.
Unfortunately it has to be one stat at a time and it takes ages if you don't give them beans. At level 1, the island gives one EV per half hour hour, at level 2 the island gives 2 EVs per half hour and it gives 4 EVs per half hour at level 3.
That means without beans it will take 31 and a half hours to up a stat.
