"certain amount of time" is correct and usable in written English. You can use it to refer to an unspecified but limited period of time, usually when talking about completing a task. For example, "I will need a certain amount of time to finish my research."
"We take a certain amount of time for the Olympics.
It takes a certain amount of time to make them.
I only had a certain amount of time left.
Investigations take a certain amount of time, Ms. Smith said.
"People only have a certain amount of time".
Each action requires a certain amount of time to complete.
Arrival in Sochi itself took a certain amount of time.
He spent a certain amount of time listening to jazz on Fifty-second Street and a certain amount of time at more social night clubs.
"Given a certain amount of time, they weren't going to be around anymore".
Broadcasters must allot a certain amount of time for educational television.
With the passage of a certain amount of time, all the frantic nonsense falls away.
Thanks to Ludwig my first paper got accepted! The editor wrote me that my manuscript was well-written
Listya Utami K.
PhD Student in Biology, Bandung Institute of Technology, Indonesia