<?php
$timestamp = mktime();
$today = date('l', $timestamp);
$yesterday = date('l', strtotime('-1 day'));
$time = date('g:i:s', $timestamp);
echo "
SELECT COUNT(*)
FROM Shifts
WHERE (start_day = LOWER('$today')
AND start_time < '$time'
AND end_time > '$time')
OR (start_day = LOWER('$yesterday')
AND start_time < ADDTIME('24:00:00', '$time')
AND end_time > ADDTIME('24:00:00', '$time'))
";
?>