It might have been Warren Buffett or Charlie Munger, who gave this really good pirce of advice - I am paraphrasing here.

Write down 20 things that you need to do. Rank them in order of importance. Cross out everything except the top 2. That's what you need to focus on.

Makes sense. For instance, when I write, I try to do it in 3-hour chunks. It takes maybe about 30 minutes-1 hour to work up to that "flow state" and that might last another 1.5-2.0 hours. You'll never get into that flow state if you fragment your time across too many activities.