Sampling Rate

Hi, I have an issue with regard to CO2-metering in practice. An important question coming on my mind - and probably a way to reduce cost when applying CO2-meters in high densely rooms - is; what is the proper sampling rate when monitoring the CO2-levels? I know that LEED Reference Guide refers to a permanent monitoring system, but as far as I know the term “permanent monitoring” is not put into the context of time. No distinction is made how long to monitor CO2-levels or what the maximum interval for monitoring should be. For me it is a bit strange to call a ventilation system improper when it fails to maintain a minimum ventilation requirement or maximum CO2 level in a room on instantaneous measurement. Imagine what the alarm system would do than. Of course the exposure time and CO-levels are inter-related and so the CO2 effects on human-being. Please advise. Thanking you in advance. Regards, Ehsan