Assuming you have a custom datetime field with the slug ‘date_time,’ here’s how you can show the date and if the date is today or tomorrow, show that instead:

<?php

// The event date
$eventdate = strtotime(get_field('date_time'));

// Today's date
$today = strtotime('now');

// Tomorrow's date
$tomorrow = strtotime('tomorrow');

// If event date is equal to today's date, show TODAY
if (date('m-d-Y', $today) == date('m-d-Y', $eventdate)) {
	echo 'Today';
}

// If event date is equal to tomorrow's date, show TOMORROW
if (date('m-d-Y', $tomorrow) == date('m-d-Y', $eventdate)) {
	echo 'Tomorrow';
}

// If event date is not equal to today's or tomorrow's date, print the date
if ( (date('m-d-Y', $today) != date('m-d-Y', $eventdate)) && (date('m-d-Y', $tomorrow) != date('m-d-Y', $eventdate)) ) {
	echo date('M j', $eventdate);
}

?>