A customer may cancel an order whilst still in their 'worry free' period. 

This is calculated by whichever is first:  

The delivery time minus the your notice period or up to one (or two for orders over £750) working day(s) prior to delivery. Non working-days such as weekends are excluded. For example: an order for Tuesday at 12:30pm with an order that required a 24hr notice period would have it's worry free period end on Monday at 12:30pm as the delivery time (Tues 12:30pm) minus the notice period (24hrs) is earlier than the the end of the working day before the delivery (Mon 6pm).