Yes, I'll still be there by 7pm just for diner (served at 6pm). Even if food is horrible, it's still ... free. Depending on ambiance, might leave by 8pm.
It is true that, in principle, there is a maximum number of girls between 5pm and 10pm when 2 shifts are present at the same time. However, that doesn't necessarily mean that there is more choice because the best ones will always be in the rooms all the time and it's difficult to catch them. In addition, June 18 is the last day of a Trade Fair and there will be lots of customers coming in after 5pm, so the ratio girls-clients may turn to the client disadvantage. Last, the girls will hurry in a session to come back to the lounge for more business.
In the morning or early afternoon, girls are fresh and are not in a hurry. Rather than waiting bored in the lounge with lots of other girls and only a few clients, they stay more easily longer in the room with you and provide better services, because morning customers are usually local and repeat customers who bring them repeat business if they are good (as opposed to occasional clients from Trade Fair who never come back so they can afford to rush the session).
So I always come early and leave early, before the main crowd arrives.
But don't worry, if it's your first FKK visit, I'm sure you'll enjoy it, at whatever time you come.
Jim