How busy is my gym?

I use a gym in the City of London, near where I work. The locker rooms have floor to ceiling lockers, in 2 banks, one above the other. I tend to use the lower bank. When I'm changing after my workout and shower (and hence need to have the locker open for the longest time), very often the chap who has the locker directly above mine, on the upper bank, turns up as well, usually after having showered too. As there's only just enough space for one person, one of us has to wait. This tends to annoy me a lot. This leads me to ask - just how busy is my gym anyway? The odds that the bloke with the locker above mine turns up to use his at the exact time I want to use mine must be quite small, unless there's a huge number of people using the gym...

Anyway, here's the first question - how many people are at my gym?

• Assume that of the 250 or so lockers in the men's locker room, anyone who turns up is equally likely to use any one of the lockers.
  
• Someone turns up at my locker, competing for space, about 70% of the time.
• Then the number of lockers in use at the men's locker room at any one time (when I tend to go) is 0.7*250 = 175.
• Add in another 175 women, then at any one time there are 350 people at my gym.

That's not all - how many people come in and out of the locker room?

• Say that the peak period is 2 hours at lunch time.
• Then say the average workout takes 45 minutes.
• Then over 2 hours there are 175*3 = 525 men coming in and out of the men's locker room
  
• Then at any one time there are 4.375 people coming into the men's locker room.

The problem is, only about 2 people come in per minute at the busiest times, and there are perhaps 150 people at most (including ladies) in the gym at any one time!

I guess I'm just unlucky, or maybe I use really popular lockers.