What is the general rule for setting the target date of the next milestone?

I don't think we really use target date. Maybe we can discuss a target release cadence? For instance, for ADBC I've been trying to hit ~6-8 weeks (it tends to slip though because I have limited time)

I'm favor of predictable release pace but flexible.
For the community, it's great to know in advance when a release is planned. However, we should clearly state that what is in the release could change (depending of resources, priority, etc).

I'm happy to volunteer for arrow-Java release every 6-8 weeks.

Maybe we can trade off to reduce the burden/improve bus factor, but that sounds good to me.

Do you want to start a small discussion on the ML? Or if we're in agreement here then let's just go with it.

Sure. I think it makes sense to discuss on the ml. Let me start a thread. Thanks !

Releasing arrow-java every 6-8 weeks sounds a little bit frequent to me. Perhaps we can start with a three-month release cadence same to the mono repo in the past.

Yes, let's start with quarter releases. We can always do intermediate release if needed.