Here is what I want to do on my existing WP site [login to view URL]
1. We will create a pop up once someone land of the website, which says book your whatsapp call.
2. Will create a button for every product to book a watsapp call.
3. Once the button is clicked it will have a small calendar as you mention along with the other info
4. Create the banner for the home page about the watsapp call thing, here is an example [login to view URL]