Although DatePicker cannot specify time units smaller than day, so sets them to zero, it would be good to leave them as they are and render properly inside HTML text field, meaning, only to affect time units larger than zero. Tapestry would practicaly get component for setting date and time, which I find terribly needed, in a way that user could pick date, and have to manually set time.
Currently, setting DatePicker with pattern such as following :
<input jwcid="@DatePicker" value="ognl:fooTime" translator="translator:date,pattern=dd/MM/yyyy HH:mm"/>
Produces HTML text field populated with something like: