We will first be upgrading servers that are already running PHP v5.3 to the newer PHP v5.3.21 which will give customers on the old v5.2 servers time to modify and prepare, and we can also move your website to the newly upgraded server so that you can test it out and resolve any issues before being moved back to your existing server.
So, Monday 4th Feb onwards, please don't ask "When will my server be upgraded" as we will be emailing you separately all to let you know which day it will be done :-)