Time frame is PDT, like the server.
Many folks want answers about exceptions & non-Pokémon avatars... really we're not going to have time to answer those individually, post 1 & 2 pretty much say it all in terms of type of Avatar & limits on lettering. Lettering is iffy in general, because its hard not to do an ugly job...
The TC consensus that created this new guideline is that it is not just non-bad avatars that are OK, but Pokemon related Avatars that are required... As Pop said, its partly because some members had their fun with sexual violence and porno references in their avatars. The other half of it, which we discussed at length is this -- the avatars ARE the graphic decoration for these Pokemon boards, so the non-Pokemon ones go on the general social networking websites, not here. This has been up in the FAQ for weeks.