Based on the clue 'a period of guard duty in the navy one may be 4 or...', what is the answer?

Based on the clue 'a perfusionist operates the medical machine named ...', what is the answer? Based on the clue 'a perihelion is the point in the orbit of a planet...', what is the answer? Based on the clue 'a period around which organizations plan budgets i...', what is the answer? Based on the clue 'a period is one of 4 major units of geologic time ...', what is the answer? Based on the clue 'a period of pregnancy or a time for the developmen...', what is the answer? Based on the clue 'a period of regulation play in the national hockey...', what is the answer? Based on the clue 'a period of silence during a radio broadcast', what is the answer? Based on the clue 'a period of the mesozoic era was named for this mo...', what is the answer?