The original question on my mind was , "how to slow down time" but after googling it, watching youtube videos and reading the question asked many times on reddit, it seem the question is worded incorrectly most of times its asked.
Most answers and suggestions to the question "how to slow down time" is basically, do more new things, create new memories. i would argue that is almost the opposite, cram in a lot of new things in a day would make time fly even faster. but at the end of the day you look back, and have a lot of new memories, which could be a positive i guess. but it did not slow down time. the closest good answer i found was more jokes, such as sit in a doctors waiting room for no reason, watch paint dry, listen to a very boring person talk....
the question is instead, how to be more aware! of time. the only solution I have come up with is to set an alarm on my phone every 30 minutes or so, just to let me mind know, "oh yeah, another 30 minutes gone, reflect.. and continue" but that would probably drive one insane after a short while.
sorry for the long post, just had to explain what the questions is not!
Any suggestions?
In short, my advice is to "make incompressible memories". Your brain collapses similar experiences into each other. Frequently change everything about your life.
I tend to group major life changes around (1) family/work, (2) yearly themes, and (3) "characters". Every year or two I get a radically new haircut and wardrobe and immerse myself into an imaginary role. My last phase was "mullet man" and now I'm a "europop DJ" haha
Also as primitive and out there this might sound but look at the sun, take a mental note of where it's at in the sky, how your surroundings are lit by it, face north or south, look at your shadow, and look at a clock as a marker. Now looking at the clock might sound like a cheat but it's to build a mental relationship with where the sun is in the sky along with a unit of measure that's not jabbing a stick in the ground. (that's what looking at your shadow is for)
Probably took me a good amount of years to be good at guessing the time with on and off practice. Also by making it a game when someone asks you for the time, to just guess and then look at your phone to see how close you were. With daily practice you'll pick it up right away.
edit:
To add to more to this. Maybe playing with your perceptions in order to dilate your sense of time might be a route to explore.