The month that you pick cherries depends on when the cherries were planted.
Usually though most cherries are usually starting to flower around April or May after the last frosts occur and then by August or September they may be ready to pick.
But you'll know when the cherries are ready to pick when the color of the cherries become completely red and firm and sometimes they may be ready to pick as early as June or July but it can vary as to when they begin to grow and produce the cherries.
The climate also determines the time when cherries are ready to be picked so there's no way to say for sure in your climate when your cherries will be ready to pick.
Just watch for them to become red and firm and then they should be ready to pick which sometimes happens as early as June and sometimes as late as July or August.