使用PHP生成具有连续时间的表

I am trying to write a site that generates a schedule. The left hand column of the table should display times starting at 7:00 am and increase by 30 minutes with each row. I'm not sure how to increase the time by 30 minutes. I can only display the current time:

CODE:

<table>
<tr>
    <td></td>
    <td>Monday</td>
    <td>Tuesday</td>
    <td>Wednesday</td>
    <td>Thursday</td>
    <td>Friday</td>
</tr>
<?php
    $p=0;
    $r=7;
    while($p<30){
        echo "<tr><td>";
        echo date('g:i a');
        echo "</td></tr>";
        $p++;

    }
?>
</table>

The date() function has an optional second parameter for a timestamp.

If you know the time of 7am for a given day (using something like mktime), then you can add increments of 30 minutes to it. Because timestamps are in seconds, you'd be adding (60 * 30) for each increment.