There is no set length of time it should take to write a screenplay, but professional screenwriters are often given deadlines they have to meet, so being able to write quickly and efficiently is certainly an asset.

Feature deals usually allow for a 12-week writing period for the first draft, but the deadline is often flexible. TV writers are often asked to turn around an episode in less than a week.

In a 2008 blog post, John August says this:

I’m hesitant to give a firm number for how many weeks it should take to write a script. Every project is different. [...] [T]he better question to ask: How quickly should a professional screenwriter be able to turn around a script, given some urgency? In my experience, the most successful screenwriters are the ones who are able to accurately estimate how much time they’ll need. [...] For feature films, I’d be reluctant to hire a writer who couldn’t deliver a script in eight weeks.

Источник: How long should it take to write a screenplay? | Screenwriting.io.

A treatment is essentially a prose version of your screenplay, although its exact definition can vary from person to person. Usually, treatments differ from outlines in that they look more like short stories where outlines look more like breakdowns or bulleted lists, but this is a bit of a generalization.

Most feature treatments are around 10-20 pages, but they can be longer or shorter depending on what the story demands, and what the treatment is for.

The johnaugust.com library has examples of various pre-script story breakdowns and outlines, including a treatment for the Alaska pilot.

Источник: What is a treatment? | Screenwriting.io.