Just a code update. Had to wrap the dates being compared with a strtotime function:
<?php
if (strtotime(Date('d M Y', $mon)) < strtotime(Date('d M Y')))
echo "Sorry no more orders for today";
elseif (strtotime(Date('d M Y', $mon)) > strtotime(Date('d M Y')))
echo '<input type="image" src="WA_eCart/Images/Pacifica/Btn3_EN_addtocart.gif" border="0" value="Add to Cart" name="teacherslunchbox_21_ATC" >';
elseif (strtotime(Date('d M Y', $mon)) == strtotime(Date('d M Y')))
if (Date("Hi") + 300 < "900")
echo '<input type="image" src="WA_eCart/Images/Pacifica/Btn3_EN_addtocart.gif" border="0" value="Add to Cart" name="teacherslunchbox_21_ATC" >';
else
echo "Sorry no more orders for today";
?>