The downtime is estimated to be from 21:30 UTC on April 3rd (actually 10:15, as I have to shut down the server *before* the move) until 3:00 UTC on April 4th.
Here is an excerpt from the email:
Just thought y'all should knowDear customer,
The new Hetzner Online Data Center Park in Nuremberg is one
of the most innovative and energy-efficient data centers in Germany.
In comparison to the current Data Center 6, the new Data Center 1
provides even higher availability and security. Furthermore,
free technical support will be offered around the clock in the near
To ensure that you too will be able to take advantage of these benefits,
we are planning to move the following servers in the night of
3. April to 4. April 2012:
The above-mentioned servers will not be accessable from 10:30 pm until
approximately 4:00 am.
PS: In case you're wondering why I said 9:30 PM to 3:00 AM instead of 10:30-4:00, the times in the email are not UTC, they are CET (Central European Time, which is 1 hour ahead of UTC)