It's a capsule hostel and if arriving in JAL business/first, you can get the shower for free with the boarding pass (possibly only applicable if landing in NRT).

Water pressure is amazing. They'll give you a key for one in a row of lockers where luggage can be stored during the shower. I've never been told an explicit time limit but there's nowhere to lounge anyway so I can't imagine it taking more than half an hour. Maybe an hour if a lot of post-shower makeup, hairstyling etc. is happening.