As you may have noticed, humans don’t perceive time passing at a constant rate. “Time flies when you’re having fun,” we say, or “the meeting was only an hour but it felt like an eternity.”
This phenomenon has obvious relevance to transportation and urban design. It’s well established, for example, that a walk seems to take less time if it’s more pleasant. Countless studies have established this as a matter of human psychology, and you probably also know this from your own experience.
But when the behavior science literature talks about improving perceived time, we should pause before deciding that this is the kind of time that matters.
As a transportation planner who sometimes works with architects, I often have this conversation:
Me: “If you design it that way, these people will have a 15 minute walk.”
Architect: “But it’s a beautiful walk, so it won’t feel like 15 minutes.”
The architect’s implication is that perceived time is what’s real. If a walk is so pleasant that it feels like five minutes, then you won’t notice that it’s actually 15.
Well, maybe you won’t, but the people waiting for you will. If you have to punch a timeclock at work, try telling your boss: “I’m not really late, because my perception of time is that I got here ten minutes ago.” For that matter, try telling that to the friends waiting to meet you, or to your spouse or child at home.
Perceived time is a crucial dimension of the human experience, and an important source of joy. Perhaps you have had the pleasure of just wandering, in a city or wilderness, without goal, deadline, or destination.  You just walk, drink in the sensations of the place, and when you come to a place where you could go one way or another, you go whichever way feels right, without regard to where you will end up. But important as these experiences are, they always end in ways that throw you back into objective time. The sun sets, or a business you need is about to close, or you have to meet someone.
Perceived time can be a great experience, and there’s nothing wrong with it, but it could also be called selfish time. Objective time, by contrast, could also be called social time. Social creatures cannot all live by their own clock. It is only by respecting objective time that humans can show up for each other in all the ways that make jobs, friendships, and families possible.
There is an obvious class dimension to this issue. If you make a trip longer in order to make it more pleasant, you’re imposing delay on people who can least afford it. When we decide to sacrifice low-income people’s objective time to improve their perceived time, we are measurably reducing their access to the things they need, thus measurably impoverishing their lives. To avoid these impacts, a logical and just approach to design and infrastructure would first focus on making the best use of people’s objective time, and only then, in cases where objective time is not at stake, work to improve perceived time.
So behavior science thinking is always at serious risk of elite projection. When someone says that a journey can be longer as long as it feels faster, I always ask, “for whom will it feel faster, and is that the only person who matters?”
 The French call this activity flânerie, and the person doing it a flâneur, a word that has come over into English in literary and urbanist contexts.