If they are WordPress experts like you say, they shouldn't stop at only installing Wordpress SEO by Yoast plugin - there are security plugins, backup plugins, analytics plugins, cache plugins, social involvement plugins that are on the "essential plugins list" of every WordPress expert and when they care about their work they will add them without doubt.
Also, installing some premium Themes require more work then simply uploading the files to the server and hitting the "Activate" button.
WordPress install alone is a 5 sec job as we all know, but a robust installation of needed plugins and theme settings can take longer.
Even so, 40 hours looks a little too much in my opinion. You should ask for details.