[meepmorp]

I think it's 30 days of diving, not 30 continuous days submerged. You can use it a whole month before you need to take a maintenance day.

There's a 3d panorama view of the interior of the sphere linked from the article - I doubt anyone's spending more than a day in there at a go, let alone with someone else.

Edit: apparently, it's 3 people - the pilot and 2 scientists.