If you already have a value in the field and you want to increment the date by one day, then use this:
UPDATE your_table SET order_date = order_date + INTERVAL 1 DAY
you can add a WHERE clause if need be...
If you are trying to insert the current date plus one day, then do this (you don't need to create $date1 in php)
INSERT INTO your_table (order_column) VALUES (NOW() + INTERVAL 1 DAY)
you can add in your other columns, too.
If neither of these help, please explain more what you want...
---John Holmes...