Converting date string to unix timestamp

[Karl DeSaulniers <karl@xxxxxxxxxxxxxxx>]

Hello everyone,
Got a quick one (I hope), and probably an easy one.
For some reason it is eluding me at the moment.
Hoping someone can help.

I am building an ics file with PHP and the form that is submitting to  
create this ics file has a jQuery date picker on it.
The date furnished comes to me like this "Saturday, January 1, 2012",  
and a time furnished like "4:20 pm" with no seconds.

Now for the ics file, I need the date/time combo to be..

Ymd\THis\Z  or in the case of the above date and time, 20120101T042000Z

Here is the block of code that I am using for this.

CODE [
...
}
else {	
	$dt_start = $_POST["field20"] ? $_POST["field20"] :  
$_POST["field21"];  //Saturday, January 1, 2012
	$dt_end = $_POST["field22"]; //Saturday, January 1, 2012
	$t_start = $_POST["field24"]; //4:20 pm
	$t_end = $_POST["field25"];  //5:55 pm
	//date_default_timezone_set('UTC');
	try {
		$start_DT = new DateTime($dt_start . " " . $t_start);
		$st_date_fmt = new DateTime($start_DT->format("l, F d, Y\TH:ia T"));
		//$startdate_stamp = strtotime($st_date_fmt);
		$startdate = $st_date_fmt->format('U');
		//$startdate = date('Ymd\THis\Z', $startdate_stamp);
	}
	catch (Exception $e) {
		trigger_error("startdate error: " . $e->getMessage(), E_USER_ERROR);
		exit(1);
	}
	try {
		if(empty($dt_end)) {
			$enddate = $startdate + (60 * 60); //If no end date provided,  
enddate is 1 hour after startdate.
		} else {
			$end_DT = new DateTime($dt_end . " " . $t_end);
			$end_date_fmt = new DateTime($end_DT->format("l, F d, Y\TH:ia T"));
			//$enddate_stamp = strtotime($end_date_fmt);
			$enddate = $end_date_fmt->format('U');
			//$enddate = date('Ymd\THis\Z', $enddate_stamp);
		}
	}
	catch (Exception $e) {
		trigger_error("enddate error: " . $e->getMessage(), E_USER_ERROR);
		exit(1);
	}
	$stampnow = date('Ymd\THis\Z', time());
	//$datestampnow = strtotime($stampnow);
}
...
]

I have a feeling I am mixing something up on my own, but I have been  
staring at this code to long to see it.
Can anyone help me please? Like I said, this is probably an easy one.

TIA!!

Best,

Karl DeSaulniers
Design Drumm
http://designdrumm.com