I am a BA Dance student from the University of Lincoln. It’s not necessarily ‘when you should start revising’ but more ‘what skill sets will you use to revise with’
In terms of remembering things long term, I recommend making mind maps, flashcards, quizzes or summary tables of the key information that you want to remember
These will not just be a one time use but if you make any of these in advance, you are able to use them quickly in the short-term to recap information
For example, if you make a mind-map about the Key events that happened in Russia between 1914-1918, then you could use this as a mini revision guide. It may be you could stick this up on your wall at home and test yourself on a mini question every day, or you could have it next to you when practicing a past paper as a memory prompt
Remember everyone is different and you have to find the best way that works for you when it comes to revision but little and often has been shown to be far more effective in the long run than cramming everything in 2 weeks before
I hope this helps!