Rewards accumulated till last date of a month are paid in next payout cycle generally beginning 5th of each month which can take several days to finish. You can see in the edit of this post that ads payments began processing on 5th May and concluded on 12th (You received your on 11th)
If you enabled ads at any time during a month your earnings will be processed in the payout cycle of next month. (even if you enabled ads, say, between 1-4 June before payouts of the month begin, you will receive your earnings only in the payout cycle of next month i.e. July)