For imagining how long it will take to get a piece done, guesstimate a time (1 hour? 2?) a multiply it by 4. This can help you account for distractions and give you a good baseline for setting a deadline.
Agreeing on gesture drawings. Only, instead of starting with 10 minutes and getting shorter, I'd start with 30 seconds x 10, 1 minute x 5, 5 minutes x 2, and 10 minutes x 1, once a week. Where do you get stuck the worst in details?
For distractions, you can set yourself a timer (pomodoro timer online can work.) this method challenges you to spend X time focusing in order to earn a break. Eg) work for 20 minutes, earn a 5 minute break. Every 4 times you've worked, take a 20 minute break. Obvs if you are very distractable you might want to start 5 mins on, 5 mins off. The idea is to build a practice (like exercising or learning music!)
Overall, try thinking of this practice and personal work as process based. The commissions are recitals of the practice you've done, but not all practice can be a recital, neithee are you getting much out of your practice if you're constantly wandering off and then doing a very tiny piece of the puzzle over and over.
Don't kick yourself for failing process stuff, but be consious of when you're straying and gently guide yourself back. Always let yourself start fresh the next day with intention to succeed.