The date type combines a date value and time value. You would give a variable of this type a value in the following way:
<cx:let name="d" value="2005-02-05 10:45:32 +0100" invoke="dateValue">
... $d contains a date value ...
That the date format is determined by yyyy-mm-dd, the time format by: hh:mm:ss and that a time zone must be specified. For central Europe time you would specify: +0100.