I actually post there already - my fics get posted on AO3 first because I have a weird thing about editing. I like to do it on their site because reading it in a different space (IE not in Scrivener or Word) helps me read things differently and finds problems easier?
I don’t post things that much in advance there, though. A couple hours, if that. But it might be easier to find stuff on AO3 than here because frankly my fic pages on tumblr are a bit of a mess and a pain to keep updated since I NEVER STOP WRITING. Anyway, that’s more info than you needed, but… :)