$currenttime = strtotime(date("h:i:s A"));

$cutofftime = strtotime(date('h:i:s A', strtotime(date('d-m-Y') . ' + 16 hours')));

$deliverydate = date('d-m-Y', strtotime(date('d-m-Y') . ' + 2 weekdays'));

if ($currenttime>$cutofftime) {
    $cutofftime+= 86400;
    $deliverydate+= 86400;
}

$interval = date('H:i:s', mktime(0, 0, $cutofftime-$currenttime));

<div>For delivery on <?php echo $deliverydate; ?> order within the next <span id="time"></span> minutes!</div>

<script>
function startTimer(duration, display) {
var timer = duration, hours, minutes, seconds;
setInterval(function () {
    hours = parseInt(timer / 60, 10)
    minutes = parseInt(timer / 60, 10)
    seconds = parseInt(timer % 60, 10);

    minutes = minutes < 10 ? "0" + minutes : minutes;
    seconds = seconds < 10 ? "0" + seconds : seconds;

    display.textContent = minutes + ":" + seconds;

    if (--timer < 0) {
        timer = duration;
    }
}, 1000);
}

window.onload = function () {
var time = <?php echo $cutofftime-$currenttime; ?>,
    display = document.querySelector('#time');
startTimer(time, display);
};
</script>

<?php
$currenttime = strtotime(date("h:i:s A"));
$cutofftime = strtotime(date('h:i:s A', strtotime(date('d-m-Y') . ' + 16 hours')));
$deliverydate = date('d-m-Y', strtotime(date('d-m-Y') . ' + 2 weekdays'));
if ($currenttime>$cutofftime) {
    $cutofftime = strtotime(date('h:i:s A', strtotime(date('d-m-Y') . ' + 40 hours')));
    $deliverydate = date('d-m-Y', strtotime(date('d-m-Y') . ' + 3 weekdays'));
}
$interval = date('H:i:s', mktime(0, 0, $cutofftime-$currenttime));

?>
<div>For delivery on <?php echo $deliverydate; ?> order within the next <span id="time"></span> minutes!</div>

<script>
function startTimer(duration, display) {
    var timer = duration, hours, minutes, seconds;
    setInterval(function () {
        hours = parseInt(timer / 60, 10)
        minutes = parseInt(timer / 60, 10)
        seconds = parseInt(timer % 60, 10);

        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;

        display.textContent = minutes + ":" + seconds;

        if (--timer < 0) {
            timer = duration;
        }
    }, 1000);
}

window.onload = function () {
    var time = <?php echo $cutofftime-$currenttime; ?>,
        display = document.querySelector('#time');
    startTimer(time, display);
};
</script>