gistfile1.txt

// http://stackoverflow.com/a/5727346/3774582
// Parse CRON frequency
// Break it down like James Brown
function parse_crontab($time, $crontab) {
    // Get current minute, hour, day, month, weekday
    $time = explode(' ', date('i G j n w', strtotime($time)));
    // Split crontab by space
    $crontab = explode(' ', $crontab);
    // Foreach part of crontab
    foreach ($crontab as $k => &$v) {
        // Remove leading zeros to prevent octal comparison, but not if number is already 1 digit
        $time[$k] = preg_replace('/^0+(?=\d)/', '', $time[$k]);
        // 5,10,15 each treated as seperate parts
        $v = explode(',', $v);
        // Foreach part we now have
        foreach ($v as &$v1) {
            // Do preg_replace with regular expression to create evaluations from crontab
            $v1 = preg_replace(
                // Regex
                array(
                    // *
                    '/^\*$/',
                    // 5
                    '/^\d+$/',
                    // 5-10
                    '/^(\d+)\-(\d+)$/',
                    // */5
                    '/^\*\/(\d+)$/'
                ),
                // Evaluations
                // trim leading 0 to prevent octal comparison
                array(
                    // * is always true
                    'true',
                    // Check if it is currently that time, 
                    $time[$k] . '===\0',
                    // Find if more than or equal lowest and lower or equal than highest
                    '(\1<=' . $time[$k] . ' and ' . $time[$k] . '<=\2)',
                    // Use modulus to find if true
                    $time[$k] . '%\1===0'
                ),
                // Subject we are working with
                $v1
            );
        }
        // Join 5,10,15 with `or` conditional
        $v = '(' . implode(' or ', $v) . ')';
    }
    // Require each part is true with `and` conditional
    $crontab = implode(' and ', $crontab);
    // Evaluate total condition to find if true
    return eval('return ' . $crontab . ';');
}