Plasma level time studies typically require serial blood samples to be taken over a period of hours, depending on the pharmacokinetics of the drug being studied. The time period can vary depending on factors such as the drug's half-life and the dosing regimen used. Typically, blood samples are taken at regular intervals, with the first sample taken immediately before the drug is administered. Subsequent samples are then taken at predetermined time intervals after administration, allowing researchers to monitor how the drug is absorbed, distributed, metabolized, and eliminated by the body over time.