Date selection and date format in MSSQL

i have to make a select transaction with a microsoft SQL db. I have to select the entry in a given range of time. So i've made my little form with the datepicker of jquery. The datetime field in the database has this output:

 Jan 1 2014 12:00:00:000AM

This is the format of the jquery datepicker:

{dateFormat: 'M dd yy'}

WHen i receive the GET call (but i've tested even with a POST and the output is the same)from the form i add the hours to the date (I'm using Zend framework 1.12):

    $startdate= $this->getRequest()->getParam('datepicker');
    $startdate= $startdate." 12:00:00:000AM";
    $enddate= $this->getRequest()->getParam('datepicker1');
    $enddate= $enddate." 12:00:00:000AM";

But it probably is not the right one as my select query:

SELECT [Document No_],[Sell-to Customer No_],[Planned Delivery Date],[Description],[Description 2] FROM dbo.SyncroPlanningTable WHERE CAST([Planned Delivery Date] as datetime)>='".$startdate."' AND CAST([Planned Delivery Date] as datetime)<='".$enddate."' ORDER BY [Planned Delivery Date] ASC

doesn't give any output. What am I doing wrong?