What is the most accepted time for a pre-tenure move?
I think the answer is "when you find a good opportunity."  I have a slightly embarrassing amount of experience in this regard, as well as some experience on the other end of things viewing such applications.  My experience is that they will not care where you are in your tenure review process; the advice about moving pre- vs. post-tenure is mostly just because there are usually more internal barriers to hiring someone with tenure (which still happens quite often).