Originally Posted by GUWonder

I've had to wait as long as 20-60 minutes for a shower to come available
for use again (after prior user finishes with it and it gets cleaned); but more commonly I've had to wait 0-15/20 minutes before one becomes available.

The wait depends on the place and time of day. More times than not, I have been lucky to not have to wait longer than 0-10 minutes. I make a habit of going to register for a shower before I decide to make use of the other facilities in the lounges.