My reasoning behind this is to add some urgency to a task. Players tend to take it for granted that time in RPG's is somewhat soft; I want to run a session where it isn't.
Of course, travel time & whatnot will introduce problems. Still, it might be interesting to see what happens when things are coming down to the wire and the players want to travel from one side of the city to the other. "That's going to take you thirty minutes."
Has anyone had any experience trying something like this? If so I'd appreciate it. Also even if you don't have any experience, I'd love to hear impressions on the idea & suggestions on how to keep it running smoothly.