Substitution question

[Mack10]

My thought was to give them 3-5 secs for replaced players to leave field, and then throw the flag. But coach claimed extra kids who were on the field weren't substitutes yet because they didn't enter huddle or notify anyone that they were to come out. They just ran on the field and stood there.

Abuse of timing rule doesn't offer B much relief, since A has burned off 25 (or more) seconds. If A only had 11 on the field, I suppose they could have legally waited until the 25 seconds was almost up, then called a time-out, or waited a couple more seconds and get a DOG.