Literally, nothing is printed in "Date" field neither in folder letters listing, nor in letter viewer. Looking at original unparsed headers of letters show that they have correct dates in them. I use roundcube 0.9.1 installed through gentoo portage system. By default roundcube sticked with russian language, but now i changed it to english, and nothing changes. Also nothing changes on changing "Pretty dates" option. Apache is 2.2.23, php is 5.4.13. logs/errors file is full with lines like the one below.
[07-Jun-2013 20:44:22 UTC] PHP Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /var/www/blog.krieger.pp.ua/htdocs/roundcube/program/lib/Roundcube/rcube_db.php on line 758
-- Andrey Utkin