Hello!
If you wish to receive private Premium support, you can always ask questions here: https://tsf.fyi/contact. We guide users to the public forums for public support so more people could benefit from our time spent writing, but we wouldn’t steer users to the forums who have already reached out to us privately (though there are select cases).
To answer your question, you can enable the sitemap while you are still developing the website. When search engines stumble upon it, they may start crawling the site entirely, but they’ll constantly face unindexable pages. This may cause them not to index your site as quickly once it goes public.
So, instead of discouraging search engines via WordPress’s Reading Settings, you may also want to set “noindex” for the entire site via “SEO Settings > Robots Meta Settings > Indexing.” This will remove all the pages from the sitemap (except those that are force-indexed).
When the site is ready to go public, untick those options and submit the sitemap to Google Search Console and Bing Webmaster Tools.
I hope this helps. Let me know if there’s anything else you have questions about. Cheers!