One of the most memorable things about gaming isn’t the degree to which time flies. It’s the way in which time slows down.
Time flying is ordinary. Time flies while you’re gaming in the same sense in which you lose track of time when you’re watching a great movie, or when you get caught up in a book to such a degree that what seems like an hour’s reading turns out to be four. That’s ordinary. Everybody does that.
But when you’re gaming, there are points at which things slow down. A particular way in which the passage of moments, of thought, of all group and individual dynamics grind to a halt like some kind of remote event-horizon time-dilation effect. Things that should move forward cease to do so, and you get caught up in the isolated singularities of particular moments in a way that i don’t think is true for any other creative or entertaining pastime.
For me, that notion has always been a part of the game (both as player and DM). However, the most amazing thing about it from the perspective of trying to describe it is that it doesn’t happen on an individual basis. Rather, it’s in those moments when the group of players actually functions as a single unit (distinct from a group of characters doing the same). Whether it’s an everything-up-for-grabs final melee or a noncombat challenge that somehow manages to require a little bit of everyone’s skills to complete, there’s a sense of each moment stretching out to great lengths as everyone gets caught up in everyone else’s thinking and actions. I’ve always assumed it to be a kind of right-brain thing — cooperative strategy as a nonlinear creativity (examining the actions of everyone at the table at the same time) that works opposite to the more linear left-brain individual strategy (first I’ll do this, then I’ll do this, then I’ll do that...).
For me, it’s the difference between ‘hurry-up’ encounters (where everybody tunes out, makes small talk, et al while waiting for the player with initiative to check his sheet, look up a rule, or make his rolls) and those encounters where everyone hangs on the actions of every other player (no matter how mundane) because they see and feel the significance of those actions beyond the individual context. In that moment, I think that players actually go beyond the normal submersion-in-character and into a deeper submersion-in-party state of mind. They move past the individual and into the whole — the thing that gaming does in way no other pastime can.