Riot Games didn't announce the end date of Season 10 and pre-Season 11 start dates across social media just yet but it's not too hard to figure out how long we have for ranked rewards or before the new items kick in.
League of Legends ranked Season 10 will end with November 10, 2020. This date is easily visible in the client itself which has the countdown to the split end. You can find it on the Ranked tab in your Profile.
When the timer runs out, the ranked rewards you earned will be locked in and can't be altered anymore. This means the Victorious Lucian skin, chroma and split rewards will be decided in the moment the time runs out.
As for the pre-Season patch, it will be deployed on November 11, 2020, barring any major issues that could cause Riot Games to change their patch schedule . Also known as League of Legends patch 10.23, it will bring all those fancy item changes and the pre-Season 11 will officially start.
At this point, prepare yourself for massive balance issues since Riot are treading into a somewhat unexplored territory, which is not their first time. It is usually the pre-Season patches when these huge changes happen.
As a reminder, ridiculous things like the red smite Warwick happened in almost the same environment so don't quit the game because the testing phase is lacking balance.
That said, it is also a clean canvas for those artists who are looking to pick some creative build and either troll or carry their teams to glory.