You apparently have to click the bump button, rather than reply to your own thread with the word bump.
It worked for one sale thread I have. I went to do it in another. Before clicking bump, I deleted a post that said bump in an effort to clean up the thread. Then I tried to click bump, and it said I have 1400 some odd minutes before I can bump. So by deleting a post in my own thread, the system apparently recognized that as a bump.
According to the FAQ, the classifieds are all now 1-post. So if you have to ask a question, I suppose that is done via PM only. If the seller wants to answer publicly, they must copy/paste the question and answer into the original listing. Seems a little cumbersome, but I'm not minding the rest of the changes.