This first statement may sound a little odd but one of the hardest things for a writer to do is find time to write. Unless you a fantastically successful writer the odds are you have a "day job". So a writer needs to find balance between that world and finding enough time to push their writing career forward. I spent three years going that route before I started Rainbows and Unicorns. Sometimes it was easy to find time to write. Sometimes it was incredibly difficult. I would go through stretches where I would end up working multiple 12 to 14 hour shifts in a row and the last thing I wanted to do at night was sit down and stare at a computer. Sometimes it was physically impossible to do when you get home and have to be back to work in seven hours. But much like working out, if you break the routine it can be hard to get back the momentum. So you have to set a realistic goal for what you feel you can achieve to keep the train rolling.
Many new writers want to set a page count as that goal. They think "If I just write five pages a day I will have a first draft in less than a month." It doesn't work that way. Putting pen to paper (so to say) is only part of the writing process. I spend at least a month figuring out plot points, story arcs, beats...etc before I even attempt to start a screenplay. At least a month. Sometimes those ideas can "marinate" for six months before I feel ready to write it. So does it count if I just jot notes on a story for a half hour but don't type any pages? Absolutely. Anything that helps propel your story towards finish is momentum.
Now comes the tricky part. When do I do this? That is going to be up to you and where your prime creative time is. I wrote many of my first screenplays in the middle of the night after everyone was asleep. I thought that was just due to the needs of my day job. When I left the government and opened this company I thought "Sweet, now I can write all day". Not so. On the one hand I severely underestimated the demands of running a business (and I thought I was being pretty conservative in my estimations). But even on days when I have my desk cleared and can just concentrate on writing I still have trouble. No matter how much I try I am just not in a creative mood in the morning. It just isn't in my comfort zone. So even with writing now being my day job I still find myself sitting up at 3am (last night) writing. I just love that midnight to whenever I fall asleep time. The house is quiet. The lighting is dark. The telephone isn't ringing. No one cares that I have noise cancelling ear phones in. The internet is not constantly updating (big one). I can just sit back and let the story flow.
I'm a night person. That's who I am. I'm comfortable with it. You need to find what's comfortable for you because you need to keep that momentum going. As I like to tell my wife "Screenplay don't write themselves".