call sleep when $i is 100,200, 300 in php code example

Example 1: sleep php

<?php
    sleep(4);
    echo "Done\n";
?>

Example 2: sleep microseconds php

<?php

// Current time
echo date('h:i:s') . "\n";

// wait for 2 seconds
usleep(2000000);

// back!
echo date('h:i:s') . "\n";

?>