Details aren't confirmed yet but here's how I expect it to go:
- This forum: likely to be unavailable for several hours (probably overnight UK time).
- Metaserver: down for a shorter time (maybe an hour?), and across the transition servers/clients may use a mixture of old and new metaservers. (2.4+ servers/clients should sort themselves out without assistance; older servers will require "/metaconnection down" then "/metaconnection up" after the transition, or they will not be visible to new clients.)
- www.freeciv.org URLs will not work for a similar period.
- DNS: service should be uninterrupted, and updates should propagate inside of 10 minutes.