run code depending on the time of day

$dt = new DateTime();

$hour = $dt->format('H');

now check this $hour in your morning , afternoon , evening or night range and accordingly give the message

I thought this thread could use a nice one-liner:

$hour = date('H');
$dayTerm = ($hour > 17) ? "Evening" : (($hour > 12) ? "Afternoon" : "Morning");
echo "Good " . $dayTerm;

If you check the highest hour first (evening), you can eliminate the range checks completely, and make a nice, more compact conditional statement.

$hour = date('H', time());

if( $hour > 6 && $hour <= 11) {
  echo "Good Morning";
}
else if($hour > 11 && $hour <= 16) {
  echo "Good Afternoon";
}
else if($hour > 16 && $hour <= 23) {
  echo "Good Evening";
}
else {
  echo "Why aren't you asleep?  Are you programming?";
}

...should get you started (timezone insensitive).

    <?php
    /* This sets the $time variable to the current hour in the 24 hour clock format */
    $time = date("H");
    /* Set the $timezone variable to become the current timezone */
    $timezone = date("e");
    /* If the time is less than 1200 hours, show good morning */
    if ($time < "12") {
        echo "Good morning";
    } else
    /* If the time is grater than or equal to 1200 hours, but less than 1700 hours, so good afternoon */
    if ($time >= "12" && $time < "17") {
        echo "Good afternoon";
    } else
    /* Should the time be between or equal to 1700 and 1900 hours, show good evening */
    if ($time >= "17" && $time < "19") {
        echo "Good evening";
    } else
    /* Finally, show good night if the time is greater than or equal to 1900 hours */
    if ($time >= "19") {
        echo "Good night";
    }
    ?>