Is this a breach?
No. Article 4.7 of the FIDE Laws of Chess defines when a move has been "made". Basically when your hand loses contact with the piece moved/captured/promoted etc. Once the move has been made the opponent may make a move. This applies whether clocks are being used or not.
If clocks are being used then the move is "completed" when the player presses the clock. If the player did not press the clock then it is completed when he makes his next move - article 6.2.1 -
6.2.1 During the game each player, having made his move on the chessboard, shall stop his own clock and start his opponent’s clock
(that is to say, he shall press his clock). This “completes” the move.
A move is also completed if:
6.2.1.1 the move ends the game (see Articles 5.1.1, 5.2.1, 5.2.2, 9.6.1 and 9.6.2), or
6.2.1.2 the player has made his next move, when his previous move was not completed
When increments are used it is important that a player making a move should have the opportunity to press the clock and gain the increment. This is covered in article 6.2.2 -
6.2.2 A player must be allowed to stop his clock after making his move, even after the opponent has made his next move.
Hence if the opponent makes his move before the player has pressed the clock then the player may press the clock without making a move and it is up to the opponent to press the clock back which most opponents would do immediately in a blitz game.
So, there is no breach, no penalty.
