Upvote:1
It's recommended to apply between three months and fifteen days before the start of your stay in the Schengen area. The three-month limit is defined in the Schengen visa code, article 9(1):
Applications shall be lodged no more than three months before the start of the intended visit. Holders of a multiple-entry visa may lodge the application before the expiry of the visa valid for a period of at least six months.
For October, you could therefore apply some time in July, depending on the exact date of your trip. If you apply too early, the consulate could refuse to deal with the application (which is not so bad as a refusal, I think you should get your money back and you can always reapply later) but I guess that if you are only a few days over the limit they might process it nonetheless.
By contrast, applying less than fifteen days in advance is not explicitly forbidden. But if you apply too late, the consulate should warn you that the decision might come after your intended trip (in which case you would have paid for a useless visa).