The phrase "a defined period of" is correct and usable in written English.
It can be used when specifying a particular timeframe that has clear boundaries or limits.
Example: "The project will be completed within a defined period of six months."
Alternatives: "a specified duration of" or "a set timeframe of".
Without a written, signed employment contract for a defined period of time, the executive is left hanging in the wind.
It could take over local administration for a defined period of time and establish a charter city there.
They would not disclose, for example, whether Blackstone and Providence had committed to invest in Freedom for a defined period of time.
Unlike travel warnings, travel alerts are issued for a defined period of time around short-term events, according to the State Department's website.
Patent protection allows inventors to recoup their investments in R&D by providing a monopoly on selling any patent-protected invention for a defined period of time.
— A limited number of herbarium plant presses is available to be checked out for a defined period of time (see Collections Manager; avoid last-minute requests).
Such committees may rely on such techniques as pilot testing, analysis of costs in comparison with benefits, or provision for evaluation after a defined period of time.
Life cycle costing (LCC) is a method of economic analyzing of all costs related to constructing, operating, and maintaining a construction project over a defined period of time.
An observational cohort study is a study that prospectively follows a group of individuals who have specific features in common over a defined period of time.
"People used to be recruited into a specific role and they'd expect to do it for a defined period of, say, five to 10 years," says Neil Morrison, group HR director for Penguin Random House.
By focusing on one thing for a defined period of time — say by counting your breath, or working at a demanding task, or even reading a difficult book — you're subjecting your attention to stress.
