Finally made it myself (mostly). Even though the site has run fine for years and thousands of content items, after the update I had to change date format! Until then there was "Y-m-d H:i:s", now I use "d.m.Y" (German format) .

If you don't have hours/minutes/seconds, the plugin stores the correct date, but uses the time of saving instead of default time. I've added some lines to repair that. If anyones interested in it, place a post.

Also I think there's some trouble with having live values like "today". This is going to be my next task.

Y-m-d H:i:s should work ok, formats that are problematic are those using textual names of days or months. Also live values now, today etc should be handled ok.

Would be interesting to see why it doesn't work for you, can you ask you hosting provider to give you a list of available locales (locale -a )? Which php version do you use?