ASIS will tell you a security officer can watch "less than 10" monitors, and that doesn't mean 10 monitors with 64 images on each.
From the Red Cross Lifeguard Manual:
Breaks from Surveillance
Lifeguards should take a break at least once an hour. In
one system of surveillance, a lifeguard might spend 20 or
30 minutes at one station, rotate to another station for 20
or 30 minutes and then take a 20- or 30-minute break. In
another system, a lifeguard might spend 45 minutes at
one stand, take a break for 15 minutes and then go to
That is an interesting question, particularly since it really is not security related. More health care.
I found this link, a little dated, but it should help give you some guidance. As I read, there also are probably State Laws that govern this topic to one degree or another. Here is another relevant discussion you might use for insight.
This is also a little dated, but:
Research in the U.S. has shown human observers (of CCTV) start showing signs of viewing fatigue after as little as 12 minutes, overlooking up to 45 percent of all activity in the scenes. After 22 minutes, they overlook up to 95 percent.
Robert Moore, citing a 2002 study published in Security Oz Magazine in his article
“What are the latest trends in intelligent video and analytics?” SP&T News, June 6, 2008. See:
Granted, is was to promote the use of anaytics to alert you so you don't have to watch all the cameras all the time... Take it FWIW...
Security Analyst Mary Lynn Garcia offers some related information (by proxy) in this discussion:
How Many Cameras Can One Monitor?