meta_query compare unix timestamp

Hi,

I have changed the innerworkings of my theme to be able to make it a bit more flexible. No I have been presented a bit of a problem.
One of the modules is a event module that shows on the archive page all the events per day.

In the old situation it was just a custom field with date formatted as Y-m-d but now i have changed this to a unixtimestamp with time.

My old code was able to get query all the posts for a specific date:

<?php
        $today = date('Y-m-d H:i:s');
        $newdate = date('Y-m-d', strtotime($today . " +{$i} day"));
        $args = array(
	                'numberposts'	=> -1,
	                'post_type'		=> 'post_type_agenda',
	                'meta_key'		=> 'begin_datum_en_tijd',
	                'orderby'       => 'begin_datum_en_tijd',
	                'meta_query' => array(
                            array(
                                'key' => 'begin_datum_en_tijd',
				'value' => $newdate,
				'compare' => 'LIKE'
			    )
	     )
        );
        $the_query = new WP_Query( $args );

But now the time is also included in the timestamp, so I cant compare with a ‘LIKE’.
How is it possible to convert the value of the key to the Y-m-d format before the comparision…

Thanks,

Sem