It's not about you doing your tags. That's personal time management. What timezones effect is when your thread partners are around to respond. So even if you're threading with someone who boomerangs, you're looking at a potential day between your tag and theirs, and then again for you to tag back. Add to the mix thread partners who don't reply daily, or people who don't backtag (not a problem anymore, but I remember it from days on LJ) and being on an opposite timezone can seriously fuck with your chances of making AC. Or at least, it did before AC requirements were lowered.