At least 3 days before/in advance?

[AndyJung]

I have some questions for you, teachers.
It is recommended that you register for the seminar to be held next Friday at least 3 days _ _ _ _ due to the limited number of seats.
(a) before (b) in advance

I thought the answer is 'before'. But the book says, if before can be the answer, there has to be a particular time after before, for example, 'at least 3 days before you register.'

And one more question.

I saw her few hours ago. / I saw her few hours before.

Between these two sentences, which one is correct?
I think both are correct, but some people say second one is wrong.

Thanks in advance.

[5jj]

It's more natural to use 'in advance', but I wouldn't say 'before' was wrong.

[emsr2d2]

I would say that either "in advance" or "beforehand" could be used but I wouldn't use "before" on its own in that particular sentence.

With your other example, firstly we say "I saw her a few days ..."
I would only use "I saw her a few days ago".
You can use "before" with a different tense though. "I last saw Sarah on Tuesday. I had seen her a few days before when we went to a wedding together."