"Observation period" refers to a specific time frame during which someone closely watches, studies, or examines something or someone to gather information and draw conclusions. Full definition
«We found that three hours was a good observation period for each run,» the biologist reported. (sciencedaily.com)
The doctor told her that if things were that bad, her husband should come in for a sleep study: an overnight observation period during which various sensors are attached to a patient. (scientificamerican.com)
Some districts require a set number of formal observation periods. (educationworld.com)