The ability to conceptualize and manage time is a brain function. It is part of a larger ability called executive function (including abilities such as starting a task, sequencing through multiple steps of a task, attention to detail, organization). The center and front of the brain specializes in executive function, and everyone has strengths and weaknesses within this area.
I started to use a visual timer with my son when he was 2 years old and LOVED it! It saved me much hassle and frustration, and cut down on the "is it time yet" conversation, which of course is never ending. Children often do best with a visual timer, and so do many adults. Without the visual aspect of the timer (the red section gradually gets smaller as time disappears, and some models have an audible timer that can go off as desired when the red is gone), time is completely conceptual. You have to somehow learn to associated a certain time with the feeling of time passing. Over time, you may learn what 5 minutes feels like, or you may not.
Many adults love to use these timers too. I know many adults who use the timer to get out of the house on time in the morning. My son loved it, and would say "how much red until we need to go." I would also set it for taking turns during play (e.g., "You get to pick the game and play it until the red goes out, and then your friend gets to pick").
I am pretty efficient when it comes to time and don't typically run late; however, I also did well with the timer...usually to keep me on task before I started something else. Sometimes I multi-task too much, and don't just sit down and just focus on one thing. I would set the timer for my son to know how long I would sit on the floor and play with him, and the timer actually kept me on the floor without going to do something else. Good thing!
The model in the picture above is called a "time timer" and we purchased ours at Amazon.com.