This sort of takes off from the discussion of basic GMing skills, but I think it’s different enough to merit its own title.
It’s seemed to me for a while that there are at least three relationships between game time and player time in RPGs.
First, there’s game time that goes by slower than player time: one second of game time, for example, may take minutes to resolve for the players. One of the common examples of this is scenes of combat. Most systems I know of have combat resolved on a time scale of between one and fifteen seconds, with actions portrayed in some detail, which takes at least one dice roll to resolve, and sometimes several—and systems with a single roll often involve more work to figure out all the implications of that roll.
Second, there’s game time that’s comparable to player time, though not necessarily identical to it. A typical example of this is conversation, where the pace of character speech is fairly close to that of player speech (it may be slower, if players take time to think of what to say, or faster, if they rely on indirect discourse rather than direct, but how much slower or faster is limited).
Third, there’s game time that goes by faster than player time, at a ratio of several or many to one. This can apply to travel, where even a day of travel played out in excruciating detail will be over in less than an hour; or to work on various tasks, where a day’s work is typically a roll or two; or to character advancement, where a character might spend a week or a month in mastering a new skill and have it covered by a training montage.
A typical game has all three sorts of time, and shifts back and forth between them without players taking a lot of notice. A game focused on physical action might mainly rely on the two extremes, defined as uptime and downtime.
Being able to manage these different sorts of time, and know when to shift between them, seems to me to be a GM skill.