Our subjective appreciation off time is affected by many things. For instance if you’re surrounded by red time appears to slow, and blue makes time appear to quicken.

Our appreciation of time, space, and form are all subject to a variety of interpretations generally based on neural priming.

or are you merely not paying attention to the time? — Purple Pond

Pretty much. I wish I studied more medicine and neuroscience/cognitive science; but, my semi-educated take on the matter is that there is a perceptual shift from self-monitoring towards some external salience/reward/hedonic impulse, which typically produces a "flow" state within the mind. A little deeper, the Default-Mode-Network disengages and attention is focused on the executive function of the brain, the Dorsolateral-Prefrontal Cortex.

As an example (in this example, I'm focusing more on ADHD, and the resulting depression and anxiety, which are comorbid in the disorder), people with depression and ADHD, have a dysfunction in their ability to self-monitor and task switching from self-monitoring to rewards/salience. This dysfunction can be "corrected" by artificial means, such as stimulant use or abuse, or through elaborate reinforcing practices. Such as eliminating distracting ques or going to the same room to study, or just more simply developing a habit and conditioning oneself to study some material.

If time doesn't actually slow down when your having fun, why does it feel like it? Do you experience time going faster? or are you merely not paying attention to the time? — Purple Pond

I think we simply don't notice the passage of time.

What's more frustrating is how it seems to go more quickly the older you get.

Oh well, back to my Christmas shopping.

What's more frustrating is how it seems to go more quickly the older you get. — Terrapin Station

Well, this is true to the degree that routines are established and tasks (such as working) become repetitive. Also, memory encoding, which degrades with age contributes to the sense of time flowing faster.

The way we percieve time is a product of how happy we are or at the very least content and also we percieve time not on a scientific basis but how we feel.

Humans are driven more by feeling than logic if left up to our most basic instincts.

When we focus our attention on the time we have more negative feelings.

When we focus on an activity we generally have feelings related to whatever activity that is.

I have a theory about why this is so.

It seems to be about noticing the passage of time. Say there is an event A and you check your time. Suppose A is followed by B, C, and D. If you check your time at all of these events you feel that time is passing slowly. However if you check time only at event D then you feel time has passed quickly.

Time goes by so fast when you are alive.

What's more frustrating is how it seems to go more quickly the older you get. — Terrapin Station

It seems to me that there is a physical explanation for time appearing to pass faster as one ages. Our brains, like some other animal brains, seem to be able to track time. As we age, this facility slows down -- and time seems to speed up as a result.

Reality check: time doesn't actually change based on what your doing, unless your going extremely fast — Purple Pond

Personally, I am an expert in the field of reality and by experience I can tell you time really does speed up when I am having fun.

Time doesn't really go faster it just seems like it does because you're so focussed on what you're enjoying that you don't pay attention to the passing of time.

In ancient greek there is two kinds of time: chronos (ordered time) and eon (episodic time). With the infatuation in the world of things empirical since the industrial age, concepts that do not fit in with scientific explanations of the external world are dismissed as garbage most the time.

Episodic time continues to operate in more ways than personal experience, for example, there is Hegel's observation about the owl of minerva.