I have my share of lifetime mistakes when it comes to time management. If I think of it now, I might as well request for one big life reset.
Nowadays, I think of trying to accelerate my phase like a metered cab. There is a calendar beside me, a spreadsheet file of priorities. And when I sit to do a task, I imagine to have just started my "cab engine," thus, the meter is running. It seems to make me accomplish more than simply doing it without the thought of this limit.
I also utilize the alarm clock more. For example, I time my cooking so I won't need to watch, stir and wait. If it needs to boil at a certain period, only the clock reminds me to attend to it. It gives me spare time to do other things. The pitfall here is the mistake in encoding the timer. Other than that, practice makes perfect.
My concept here is a domestic application of PERT/CPM, where every slack has to be filled in with task for efficiency. Let us exclude the reasonable time of rest here. It is just a more practical context. It's self-explanatory. Try it!