Is it correct to say "more time"?

My teacher said today that it's incorrect to say "I need more time" in English. She said it is used widely but it is a slang. I don't agree with that as I encountered it often in English books, but after some searching in Google I didn't find confirmation or denial of this.

Could you help me, please?

Solution 1:

I need more time is perfectly grammatical and there is nothing about it to be considered as slang. Your teacher might have meant that it sounds too informal in certain contexts and you should clarify with her.

Solution 2:

I suspect your teacher objects to the concept of "needing more time" for technical reasons.

Saying you need time, implies that you can be in possession of time as if it is a physical thing (e.g. "I need more beans"). But time is not physical, so can never truely be possessed.

For that reason, she considers it to be slang.

In my opinion, this reasoning is false, since slang is not defined as such.

Here is wikipedia's definition:

Slang is the use of informal words and expressions that are not considered standard in the speaker's language or dialect but are considered acceptable in certain social settings. Slang expressions may act as euphemisms and may be used as a means of identifying with one's peers.