Unfortunately, I am guessing three months would be a minimum. The conjecture is from some I guestimated ages found in the wild and shipped to me (they may have been a month older but not younger). I looked back on some of the posts for Zyan Silver's bimacs and it appears he waited 5 months to ship them and I believe all recorded shipments survived. I have tried transporting by car (both to and from me) animals under 2 weeks and all cases failed.
That being said, if you want to try, the loss would be no worse than keeping them together and would provide more data on what we can and can't accomplish. Ship with lots of water and overnight (for any octo). I would recommend at least 1 month. I'm up for the experiment if you want to try.