It doesn't go by a case of time, as much as it goes by a case of instances and severity over games played.
If I was reported for neg attitude (provided it was noted I was actually negative in this example) in my next 5 straight games, I'd probably eat a chat restriction. If that didn't stop me, I'd eat a ban.
If I waited out the ban, and another 2-5 months to be safe, I still haven't played any games in that time...so if I start eating more reports, what's changed?
Mind you, if I were consistent enough to get it every single game, it'd be pretty easy to tell that I'm simply not enjoying the game anymore. Let alone making it less enjoyable for others.
Either way...I don't think time is the factor. I think history is the factor. That's the point to take from this.