This directory includes several Forsaken-oriented guilds in the roster, and several of them are anti-Sylvanas since that is what you’re going for on that character! The little blurbs along with the link to their guild information forum post should give a pretty good summary of what to expect in terms of storyline and what kind of content the guild generally participates in.
As for the active hours, I’m not quite sure what guilds are generally more oriented towards one timezone or another, but I know that this server has a good mix of people on a variety of timezones. I myself am CST. It is probably best to ask whomever you might contact for further details what server times the guild generally participates in activities, and see how it aligns with your IRL timezone schedule.
I hope this helps, and that you find a guild that works for you! I think you’re going to have a lot of fun here!