I arrived at the A38 club at about 6:45 AM on Sunday, registered for a shower, and here's what resulted (I'm "A. KEN", estimated wait time 94 minutes). Boarding time for my next flight was 7:55 AM from a B gate, so it did not look like it was going to work out.

At 7:30 AM I went up to the guy seemingly in charge of the showers and told him I'd need to cancel. He asked me what time my flight was and said, "well, you're next; if the shower guest in there now wraps up quickly, you have a chance". I told him, "Well, OK, and you don't need to clean it for me; I'm fine to just walk in as soon as the previous guy leaves". So I sat down nearby, and at 7:38, he summoned me. I took a very fast shower. I was out by 7:45 and made it to my gate just before boarding commenced.

Anyway, it seems to me that if an airline club is going to have showers, it ought to have a lot of them, like the non-Schengen KLM lounge in Amsterdam (which I think has at least a dozen showers). Or, make the showers "locker room style". I don't need a big fancy ultra-private shower suite. Being #2 in line and expecting a 94-minute wait is just unacceptable.