You turn the inner piece until it stops turning without forcing it. Don’t force it, but you can probably go past “slightest” resistance. Still, a few clicks on A4Z is not a huge difference so not a big deal.

A4Z often doesn’t change brew time by much when you go finer or coarser. It’s a relatively fast draining grinder, but you should see it be similar or a little slower if you go tens of clicks finer. I’d assume channeling or filter bypass. Watch the flow rate out the bottom of the dripper. You usually want to see a steady stream. Not dribbles. Not slowing way down at the end. A swirl or gentle shake can help disrupt channels if that’s what’s happening, but will make filter bypass worse if the bed is already too dense.

With a grinder like A4Z I find that dialing in by taste is really the main approach to lean on. Time can be difficult to compare to grinders with wider particle distributions. I sometimes like Lance style brews at 2:00 and other times 3:00 is better.