For example if you want to create your own an easy ( and readable ) way to do it with php is by:

$day = date( 'w' );

if ( '1' === $day ) {
	echo 'monday';
}

Where Sunday = 0, Monday = 1 so on so forth, and you simply echo your video url or code etc ( you decide that ).

You’re not giving much details to be honest to help further :]. If there’s a page with a video already on it and you want to change it’s source a link would help a lot to see how the theme is set up etc to give you a possible solution.