How long it takes to rank a website?

I know some people with their own business without a website and I'm sure they would love to have one that rank on the first page of Google.

The thing is, I never did SEO, so how long it can take?
I'm pretty sure they would buy that site from me if it shows up on the first page of Google searching 'lawyer xcity'.

The city is a small one, very little competition.

Depends on many things, but usually between a couple months and a year.

So is even hard to try selling websites..

45 - 60 days is bare minimum to see some ranking if it's a new website.

the combination '<any lucrative business> <any city in the world>' has been done to death so the competition is tough. Even if you start a new lucrative domain/service niche/whatever, you will depend on words to describe it and those words are already ranking on other sites which are in some way related to yours (<any city in the world>) so it will still be a hassle.

lawyers <any city in the world> is the same with attorneys <any city in the world> or defendants <any city in the world> and any other synonym of those words.

The online world is getting smaller with each new way of seamlessly connecting A to B.

But... if you don't manage to find another way of selling your websites you can always try ranking them through simulation... Recreate as many of your competitions links as you can

Depending upon keyword, it can be done in various ways.
You can go for quick rank boost (which may have a later downfalls) or a steady so called whitehat' way. If the keyword has low competition, first page rankings can be achieved in a month. All you need is good SEO skills, which are rare these days.

If you are new to SEO, then I would advice to learn the tricks first.