I am using Woothemes Woocommerce Bookings. I want users to be able to enter a date in the product booking date picker and have the system make the booking three weeks prior to that date. e.g. customer uses the date picker to select 28/04/2018 (28th April 2018) but the booking is made for 07/04/2018 (7th April 2018).
All bookings are made in blocks of 5 weeks (35 days) but they enter in a date that results in their booking being 3 weeks (21 days) before that date, and 2 weeks (14 days) after. Customers only select one date, there is no start and end date for them to select.