You're saying your DB field is a 'date' file type?
I don't know how that one works or what it accepts, but I would start by using the UNIX time stamp: time() and perhaps parsing the result from your JS date picker with mktime(..). You can get a readible time/date back again with date(..). For this to work, save your timestamp in an INT db type and work the magic.
I'm quite new to PHP also but I find the UNIX time stamp is usually quite easy to work with.