Hi Luke,
I’ll give you an example, I think it’s easier.
We have a plugin that allows our customers to choose the delivery day. So, we wanted to have a fixed value of 2,90€ (for example) and change it to 3,90€ or 1,90€ if the client chooses the delivery day to Saturday.
I think that what you mentioned was for the day that the order is placed, right?