Was there 2 times between 5am and 7am/8am and was very crowded. But for me the shower queue is not really a problem. Of course, would be better to come and shower directly.
But I got in the lounge and went directly to the shower counter to set me on the list. There were 14 people before me and should take about 30-45mins. So I went to the buffet upstairs and had breakfast without any rush. After finishing breakfast I headed back to the shower and was the next one in the queue.
If you are not there, they will call you and skip you on the list. When you arrive later, you are always the next on the list. So not really a problem.