Along this same thread...

[grantsrc]

I think my purpose this fall is to remove this phrase from every HS official's vocabulary. I am getting very frustrated with how prevalent this phrase has become.
To expand on what BoBo said, the common interpretation of the substitution rule is 3-5 seconds for the word "immediately."
Granted, 5 seconds is long, but just because a sub comes in and makes 12 in the huddle, doesn't mean you have a foul. Same as if 12 comes on and gets to the huddle, huddle breaks, and replaced player leaves. Not a foul. Keep one word in mind here, deception. That's the intent of the rule.