Hmmm, there seem to be a number of significant disconnects here.
First, an AutoSSL will be perfectly fine for your purpose. There's actually no difference between how a free SSL performs and a paid one. The encryption is the same. The thing is, the whole point of AutoSSL is that it is a two or three click installation process. It literally takes three or four minutes, not eight hours. Your developer must be assuming he is going to have to generate and install an old-fashioned certificate in the completely manual method that used to be necessary. That's simply not the case with AutoSSL in cPanel.
Second, the actual domain name migration is going to need to be made up of two overlapping parts. The first part is getting all of the website files and objects to run under the new domain name and HTTPS protocol. The second part is getting all of the external elements adjusted and corrected so they are also using the new domain name.
For the first part of that process, there are WordPress plug-ins that will do the basic website migration in about an hour. These plug-ins will handle changing all of the URL references to the new domain name, and updating them to reflect the HTTPS as well. Then it's necessary to do quality assurance on the site to make sure that any small exceptions or manually created URLs get caught and corrected as well.
The final step is getting the DNS and redirects in place so that all of the old domain traffic is correctly redirected to the new domain and pages. In addition, all of the external/third-party tools that are used with the site must be updated. Things like Google Analytics, Google Search Console, AdWords, ad servers and other tools must be updated to reflect the new domain name and protocol. In addition, all the external profiles you use must be updated as well for things like Facebook, Twitter etc. If your site relies heavily on Facebook share counts for social proof, there are also extra steps that must be taken to salvage those counts after the migration. And finally, you must decide how you're going to handle company email with the change in domain name. This relates to both the company email mailboxes, and the way email is handled from forms on the website.
Doing a domain and https migration like this is definitely a significant undertaking and needs a proper, well-thought-out project plan for implementation, But the actual moving of the files and website to the new domain name and HTTPS is certainly not a 30-hour process. It's managing all the rest of the elements of the migration to ensure both usability and SEO are maintained that take up the time.
Hope that all makes sense?
Paul
