[Grammar] I knocked (on) the door for three minutes before (until) someone answered it.

LiuJing said:

I knocked on the door for five minutes until someone answered it.

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Two questions if I am allowed to ask.

1---- Is the 'on' optional? No.
2---- Can the 'until' be replaced with 'before'? Yes, and I actually prefer "before" when used with the time frame. See more info below.

Thank you.

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emsr2d2 said:

My basic responses are above in red. With #2, as I said, I prefer "before" when used with "for five minutes".

I knocked on the door for five minutes before someone answered.
I knocked on the door until someone answered.

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LiuJing said:

Thank you for the distinctive explanation, and I've noticed you used 'answer' rather than 'answer it'. Does it mean my version 'answer it' sounds a bit strange and unnatural?

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