time dropdown in html

for($hours=0; $hours<24; $hours++) // the interval for hours is '1'
    for($mins=0; $mins<60; $mins+=30) // the interval for mins is '30'
        echo '<option>'.str_pad($hours,2,'0',STR_PAD_LEFT).':'
                       .str_pad($mins,2,'0',STR_PAD_LEFT).'</option>';