Dropping Punishments

Riot uses a punishment volcano system. When a punishment is issued it goes to the next punishment on the list. Severe infractions can skip penalty tiers. The most common escalations are 14 day bans for slurs or urging self harm.

Treated as a pristine account 10 Game Chat Restriction 25 Game Chat Restriction 14 Day Ban Permanent Ban

The tiers do reset after enough of a habit of good behavior is shown. It normally takes between three and 6 months of regular playing with good behavior to reduce a single penalty tier.

It can go faster for those who reform more fully or for those who play shit-tons of games, but it can also take longer for accounts that continually misbehave.

After a 14 day ban, there are 3 tiers of punishment to go down, so that would take between 9 and 18 months to be treated as unblemished. Most people are on the faster edge of this scale.

This is the wrong mindset, you're one punishment away from perma-ban hood. (If you're asking when the punishment de-escalates, it doesn't.) You should probably take a long look at what you've done to get yourself into this position and change it dramatically and quickly.