best to class them when you get your Yamato. So about lvl 85+

Depends on what you want. If you class them now they will hit the reload cap shortly after lvl100. If you wait till their late 90ies they will hit the reload cap unclassed at which point waiting longer makes no sense anymore.

I classed mine (11/11 only) at lvl92 or so, when my supports were ready to drive Yamato. I never regretted that decision. They hit reload cap shortly after lvl 100 too.

If you're using the B65 you could class them now and get direct use of them.
If you're going with the Nagato then class them when starting to drive the Yamato.

If you've never driven a BB with AA before be aware - it's not easy to do both and I see lots of BBs dying while AAing around cause they didn't recognized they came into enemys range.

can i still reach the cap if i dont class them late? i used elite bve reload and they are dp gunners now :(     NOT CLASSED LATE!

Thanks for the tips, since I'm not using B65 I'll class them at Yamato lvl.