Hello,
sitemap processing time depends on the page generation time mainly, since it crawls the site similar to search engine bots.
For instance, if it it takes 1 second to retrieve every page (it may be less or more), then 1000 pages will be crawled in about 16 minutes.
Some of the real-world examples of big db-driven websites:
about 35,000 URLs indexed - 1h 40min total generation time
about 200,000 URLs indexed - 38hours total generation time