Kudos to you for having blooms already!

Yes, they will still be blooming end of August, but sadly, they might be not quite up to standards... Aggressive watering, disbudding and fertilizing might rejuvenate them a month before showing, though.

Several serious show growers I know deliberately start their dahlias late, timing the first of the blooms for the shows. Often, they will only allow 3-4 blooms on each plant of the larger varieties FOR THE LIFE OF THE PLANT! This forces the energy of the plant into those few blooms (only one developing and blooming at a time).

For me, showing is secondary to continuous blooms, and I'd rather have a lush garden for a longer season. But, oh, those show blooms! WOW!

Cheers,
CC