Whonix 0.5.6 fixes a time zone bug, which prevented Tor to connect in some cases.
If you are using 0.5.5 already, you don't have to update to 0.5.6, if you do the following manually...
1. Power off Whonix-Gateway.
2. Virtual Box -> Right click on Whonix-Gateway -> System -> Check "Hardware clock in UTC time" -> Ok.
3. When 0.6.x comes out, this message will go away and you will be notified.