Are there any external plugins/apps that allows you to set different delivery rates based on delivery day and time slot?
For example, $10 for delivery time slots between 9am - 6pm but $20 for time slots between 6am - 9am and 6pm - 9pm. And $20 delivery fee for the whole of Sunday.
Nick here from Shopify.
There are a number of shipping apps in the Shopify App Store which would be worth your while investigating to see if they have this feature. Some of the most popular and highest rated can be seen below:
It could definitely be worth your time to take a look through these to see if one can do what you're looking for. I looked at the description for each and none of them outright mention this feature, so it could be worth adding them to your store and testing them out but also to see which ones you resonate with.
I hope this helps and points you in the right direction.
All the best, Nick