Hi,
I've just tested the time problem and with Greek language, the time is off even with SEF completely disabled. I've installed English UK (default), English US, Czech and Greek languages, and only the Greek language causes the creation time to be off, and it doesn't matter if I have JoomSEF enabled or not, or if I even disable the SEF completely in Joomla, so for me it seems that there's some problem with the Greek language pack. Are you sure that the time works correctly for you with both languages when JoomSEF is disabled?
As regards the K2 popup window, I've found a bug in system variables filtering, so go to JoomSEF's Advanced configuration and disable the "Filter system variables" option. This will be fixed in next version.