Roundcube gives you the chance to easily modify your Time / Date and Language settings. To do that, log into your Roundcube webmail client. There click on Settings in the upper right corner. Then select Preferences -> User Interface :
There you can choose from a long list of Languages , you can select Time Zone , Time and Date Format . You may also choose the Pretty dates option – if you pick this one the date will be displayed like Feb. 04, 2013 vs 2007-02-04 . You can as well select how often your webmail client will connect to the server to check for new mails.
When you are ready with your settings, just click Save and you are all set.