How do I set a percentage increase for just one day?
I still want people to be able to book in advance at our normal rates but to be quoted extra for tomorrow only.

Hi,
you can use Tariffs to have different prices for different periods of the day. You can also create Special Tariffs for specific Dates throughout the year.

Here is some more information on how tariffs work and how to set them up: https://booking.drivenot.com/en/documentation/46-tariffs

Hope this helps.
Kind regards.