How long should it take a newbie to write a screenplay?

Question from a subscriber

A subscriber sent me this question:

I’ve had a feature film idea for awhile but I’ve only just started screenwriting. How long is a reasonable amount of time to write a screenplay? (90-120 pages)

I’m sure the answer varies from writer to writer and from project to project. I can only speak from my experience. While my partner and I work almost exclusively in television, we have sold two features. (Both to 20th Century Fox.)

At the time, our day job was writing for King of the Hill, so we wrote our feature scripts at lunch, at night, and on weekends.

So how long did it take us?

Here we are before show night, looking very young.