It's like how navigating HQ works on a literalism: "It's kind of a maze, unless you hadn't noticed." If you really pay attention to the time—especially if you want it to go faster—it will probably slow down just to spite you. Otherwise, it can go really quickly or really slowly or really normally, depending on factors such as the dimensional location of the bit of HQ you're in, how much fun you're having (time flies when you're having fun, you know), and the like. Thus, for some agents it's almost exactly like Real World time, and for some it works like time in Narnia, and for some it changes daily.

The time spent in missions messes with things, too. You can spend a week's time in a fic but come back minutes after you left your RC thanks to portals. Similarly, how time passes in HQ is irrelevant to when you decide to pop back to the Real World. Though if you've aged five years, it's probably unwise to return the moment after you left.

Really, it all comes down to how you want to write your spin-off. Some folks like to write their missions as though they happen back-to-back, and some write them as though they're spaced out, assuming that the time between is filled with more routine missions and other stuff. In my case, Agent Derik's missions occur more or less back to back, and that's because he's distracted a lot. Lots of time passes between them for others, but not for him because he doesn't notice it; his aging is less obvious for the same reason. Nume and Ilraen, on the other hand, have a perfect memory and a perfect biological clock between them, so time for them is pretty much normal because they can't help but have a passing awareness of it. I have to keep track of how old they are.

Make sense? ... More or less?

~Neshomeh

Time passes, but not at the same pace as the Real World. This is why we have HST, Headquarters Standard Time. Whether this is faster or slower, I don't know. I guess it's probably alternately either one.