Hi there, apologies for the wait! I think it is safe to say that while we generally do not accept alternates, that is kind of the whole point of Sylvie and she operates independently of Loki, enough, that she could be considered her own character.

For the "canon-must-be-1-month-old" rule, it would be from the point you plan to apply -- if you want to play Sylvie from the season finale, then it would be the last episode. Applications do not open again until the end of August, so you'll be fine! :)