After you type FADE OUT.
You'll probably want to get some feedback and notes on the project before you start work on the next draft. Try and figure out what the weak areas are and hopefully find a way to improve them and make that project stronger.
I'd say a minimum of two weeks – ideally three, possibly four.
Once I'm finished with the first draft of a project, I'll try and push that story out of my head. This usually takes a month or more, during this time I'll start putting notes and ideas together for my next project. Usually I'll start work on the next project as soon as possible and push through until I've reached FADE OUT on that one as well.
You can do other things as well to take your mind off that project. Read scripts. Watch movies. Give feedback and notes on other people's work. Join a site like Trigger Street Labs. A great place to learn. Keep your mind immersed in the world of writing and movies.
I like to set myself writing goals. Ideally four, possibly five projects through the course of a year. I'll make my way through each project until I've finished the last one and then head back to that first project and start work on the rewrite. In the hopes of having a fresh set of eyes and a new perspective on it. More often than not, you'll get too close and over protective of your work and stepping away for a longer period will help in the rewrite phase.
Everyone's different, there's no right or wrong way. It might take a while, but you have to find the best approach that works for you as a writer. Through trial and error.
You have to push through and keep writing.
It's a marathon, not a sprint.