Setting new products for specific month

I want to set new products box to display a specific month without changing. For example, new products box is set to display products uploaded in June and even now it is July, the new products box will keep showing the June products.
How to achieve this? Someone told me to define a constant with SQL query, but I don't how to do this. Please help me with this. Thank you very much.

https://www.zen-cart.com/tutorials/index.php?article=3

Thanks for your reply. But I am not asking for expired date for new products. I would like to constraint the new products box to show a specific month without changing along with time.

I think I have find the define of New products as below. Could anybody help modify this code and set to show products uploaded in June? Thanks.

// get define of New Products
function zen_get_products_new_timelimit($time_limit = false) {
if ($time_limit == false) {
$time_limit = SHOW_NEW_PRODUCTS_LIMIT;
}
switch (true) {
case ($time_limit == '0'):
$display_limit = '';
break;
case ($time_limit == '1'):
$display_limit = " and date_format(p.products_date_added, '%Y%m') >= date_format(now(), '%Y%m')";
break;
case ($time_limit == '7'):
$display_limit = ' and TO_DAYS(NOW()) - TO_DAYS(p.products_date_added) <= 7';
break;
case ($time_limit == '14'):
$display_limit = ' and TO_DAYS(NOW()) - TO_DAYS(p.products_date_added) <= 14';
break;
case ($time_limit == '30'):
$display_limit = ' and TO_DAYS(NOW()) - TO_DAYS(p.products_date_added) <= 30';
break;
case ($time_limit == '60'):
$display_limit = ' and TO_DAYS(NOW()) - TO_DAYS(p.products_date_added) <= 60';
break;
case ($time_limit == '90'):
$display_limit = ' and TO_DAYS(NOW()) - TO_DAYS(p.products_date_added) <= 90';
break;
case ($time_limit == '120'):
$display_limit = ' and TO_DAYS(NOW()) - TO_DAYS(p.products_date_added) <= 120';
break;
}
return $display_limit;
}