You can use the Magento 2 Marketplace Time Slot Discount from Landofocder. I have used it for my stores and it works quite well. The support is also fast.
Here is the link and its outstanding features: https://landofcoder.com/magento-2-marketplace-delivery-time-slot-discount.html/
Outstanding features:
- Timely Get Slot Discount
- Multiple Time Discount Setting For One Product
- Detailed & Exact Time Slot Setting
- Flexible Time Range Options For Customer
- Easy Setting Time Discount For New Product
- 1 - Click Delete Time Slot Discount
- Dynamic Exchanged Emails System
- Powerful Ordering Management
- Optimized Product Searching
- Incredible Shopping Cart
- Best Management System