I hear and read people saying anywhere from once every five minutes, 20cfm , to three times a minute, 300cfm.
I personally lean towards 2-3 times a minute. However, I am striving for negative pressure to keep the odor from escaping the flow of air from my room to the outdoors.
With no odor concerns, I would agree with the above. Once a minute.
I would recommend getting a fan that is capable of twice a minute, then add a speed adjustor, and dial in the perfect speed.
This way as conditions change, you can deal with them. Also, you might want to go a little bigger one day. Unfortunately, there is no 11 on inline fans.
You should know that 100 cfm from a can fan/vortex or it's like is what I speak of when saying 100cfm.
A computer fan or booster fan is rated generously. If you are using these fans, I would go for 2 times a minute.