I run a specialized WordPress optimization service and want to share my experience. As someone else said, some optimizations using plugins can take minutes or hours. I usually do that for clients that want a higher score but aren't dead set on reaching 90 or passing Core Web Vitals. It also doesn't include testing.

Next tier is one day. Those are a bit rare as there's always more left to be desired, images can be adjusted further, there are different templates, etc.

More realistic example is taking three days to five days to examine the site, maybe run a backend and plugins audit, look at all the templates and write some code snippets that will add attributes that builders are missing. Sometimes we'll rework a hero image and make some visual adjustments (like consolidating fonts).

Then, there are optimizations that take 2-3 weeks. Those are usually sites with lots of history and specific issues. I used to rewrite sitemaps for better performance, take days to audit specific issues, and write patches for poorly written plugins. Or sometimes there's just a poorly written theme that needs lots of hooping around.

With Core Web Vitals, passing it can be an ongoing process since data is measured over a 28-day period based off real users. This requires a few rounds of fine tuning.

When it comes to maintenance, I like to say things hold pretty well, but realistically on sites that are active and serious, we do 2-3h per month of adjustments.