There is no mention of 18 days for AP, only the EAD. You must read anything from an official source really carefully, not just skim it!
But I would concur with @Crazy Cat I think, and think that the 18 days would only be applicable if you were filing the I-290B so the underlying I-485 would be re-opened. But you can always file and then try it, and if you’re now hiring a lawyer (as advised above) to help you with the new application, they’ll be able to tell you for sure.
Good luck.