If you set up holidays on the system, you'll be able to specify different prices for that days, in case your center is open.
To set up new holidays, go to Planning → Centers Configuration.
Access your centre clicking on the "Edit" button.
Once inside, on the left menu click on "Holidays". There you can create a new holiday or edit any of the ones you already have. To create it, click on the button "New" and you'll see a window called holiday record, where you can select the day and month. After that click on the "Update" button on both tabs and it's done.