Just make a blanket rule regarding how late someone can be from now on. Done.
There already are rules on this.
"If a player is going to be late for any reason, ample warning must be given to the admins. If the forewarned late arriving player fails to show within 10 minutes of the time notified by the team this will result in a walkover. A player that fails to show within 10 minutes after their match is due to begin (10 minutes after start time if the offender is the starting player. 10 minutes after the end of the previous match if the offender is a subsequent player) will be walked over."
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