When I do serious time blocks of writing, I use a modification of the Pomodoro Technique.
The classic Pomodoro Technique is a writing system in which you set a physical timer for 25 minutes in which you do a focused burst of writing, followed by a 3-5 minute break, then, after giving yourself a small check for completion, you have completed one Pomodoro. This is then repeated 4 times, at which point you take a 30-minute break. You then continue this cycle as many times as needed.
My modification is as follows: I do one 50-minute Pomodoro with a 10-minute break, followed by another 50-minute Pomodoro. ( I’ve found that 25-minute Pomodoros are insufficient for me to get deeply into a writing flow). After two 50-minute Pomodoros, I take longer breaks (30 minutes to one hour) in which I run a quick errandd o bills, etc. Then, I am back at it, doing my next two-set Pomodoros. It’s not uncommon for me to do up to eight 50-minute Pomodoros a day, which can add up to over 6 and 1/2 hours of writing. A solid day!
A few other details. I don’t use a checklist. I do use a cheap tomato-shaped egg timer (as pictured above) which has a nice ticking sound, but a slightly annoying alarm.
Also, I have tried several Pomodoro apps on my phone and iPad (all of which have a wide array of programmable options) but I have found them less satisfying to use than a physical timer. This dovetails well with my commitment to minimize my use of digital tools whenever there is a reasonable physical alternative.
Anyway, for any writers looking to experiment with different productivity techniques, the Pomodoro Technique is worth checking out.
Additional Resources:
Frances Cocirillo (The creator)
Pomodoro Technique on Wikipedia
One Tomato, Two Tomato: How I Use the Pomodoro Technique.