"spend extra time" is correct and usable in written English.
You can use it to describe an action or to make a suggestion. For example: "We should spend extra time studying for the exam tomorrow."
Spend extra time with children at bedtime.
They spend extra time on math, science and English.
They have to spend extra time and money travelling to less alluring destinations.
I was jealous of the boys who got to spend extra time with Father Al.
Next, Baffert said, Espinoza needs to spend extra time studying, speaking and thinking in English.
To keep their options open, some users spend extra time managing the format of their collections.
He vowed to spend extra time with with patient the next day, but the patient died that night.
I have found that if people think you're working really hard and trying, then they'll spend extra time with you.
Why then would you want to spend extra time squashed into the increasingly confined space of an aeroplane?
Moreover, they said, Congress will have relatively little time this year because members will spend extra time at home campaigning.
If someone else is going to be sharing the bed, spend extra time finding a bed that's mutually comfortable.
