The time flowing is a purely a mental projection.But how?
Imagine yourself in a field,
you do not have a watch
it is dark sun is not coming up
can you guess the time now?
This is an actual experiment to explain how humans experience time.Time for humans is very easy to understand,
watch a movie for 2 hours and sit down,start meditating for 2 hours.You will feel like it is 4-5 or 5 1/2 hours.
The experiencing of the flow of time is relative to what you are experiencing now.If what you are doing is exiting time is faster to your mind (Like a date with the love of your life).
But if what you are doing is boring time is slower to your mind (Like school)
So the conclusion is the feeling of time passing by is a complete illusion of mind thinking.If the mind was asleep like you do in the night you will not feel it at all.
(If there was no clock in your house can you say how many hours you slept last night?)
So what about the Past?
Past is not a real thing.Your brain can't even fully memorize a single event.What it does for this amazing magic to happen is very simple.
It is more like how you studied back in the school.
Your brain/mind remember the most important events of a memory and fill in the blanks to make the rest of the memory.But you can't find a difference between the memory and the real event.Because what your mind makes up is all you can remember.
For example try to remember the last time you went to see your grandmother.
Can you remember what shoes you were wearing?
Can you remember who you met before going there that day?
I guess you will not be able to.Brain did not recorded those things in the permanent memory.Because none of those small things were important to make the memory in the first place.