It's pretty simple - things change almost all the time.
What works today may not work tomorrow and an idea I have at a random moment can get me from spending 4 to 6 hours a day working, to working only 2 hours a day making the same amount of progress.
For example, lately I've been writing as much as I possibly can on Monday, trying to finish around ten articles in one single day, and then publish them on Steemit throughout the week in order to have more time at my disposal every day.
That helped me focus a lot more on learning how to use Blender, using Photoshop to do all kind of things and searching for multiple tools and skills I could learn that could help me improve what I do and finish my work twice as fast without putting in more effort.
Changing how I work all the time allows me to constantly experiment and see what works for me and what doesn't.
I tried waking up really early in the morning to finish all my work, and while it was nice for a few days, it just wasn't for me. I had to go back to my old habit of waking up when I'm not tired any more.
I also tried working for 25 minutes at a time then take a short break. Didn't work. I enjoyed working, but taking a ten minutes break often and play some video games... well, that was, too often, more enjoyable than being productive, and that short break always turned out to be a 3 hours quest in Witcher 3.
I even tried the 9 to 5 method a while ago, trying to see if working the way most people do will actually help me achieve my goals and make as much progress as I want to. Guess what - it didn't work. Sure, I was finishing a lot of work, but at the same time, I was so tired that I just didn't feel like spending more time after work learning and trying new things.
So, I decided to stick with deciding what tasks I need to focus on every single day, spend as much time as needed finishing those tasks and then do whatever I feel like doing, be it playing video games or learn something new.
Constantly switching between working methods and trying new things is gonna help you figure out what kind of schedule suits you best and what's the best way for you to make a lot of progress without investing too much effort into what you do.
I really advise you to try experimenting with working methods and see what works for you. Who knows, you may realize that finding a new way of doing things and working in a completely different way than you did before can help you achieve more with a lot less effort.