Is there time in space?

Ok, I guess the question I mean to ask isn't really *that* general. I don't really mean to get into a "if a tree falls in the forest and no one is around to hear it, does it make a sound?" kind of thing. (oh and YES. Yes it fucking does make a sound.)
My question surfaced when I was watching the last episode of Firefly a few days ago. In it, Mal Reynolds states at one point, "It's late; let's get some rest." HOW DID HE KNOW IT WAS LATE? This didn't really bother me while I was watching the show, but the question did come up. And it still doesn't bother me, really, but now I'm curious about the concept. Seriously, what constitutes as "late"?
Outside of their ship (when in transit) it *always* looks like this:

What time does that look like to you?
But they can have clocks that they set to a certain time! you say. Fine, yes, maybe.. I've never seen a clock anywhere on Serenity, but given this hypothetical future, that could be a way to make sure you sleep when it's "late", have breakfast in the "morning", and so forth... Even so, though, how do you pick the time? Say you're a crew similar to that of Serenity in this exact same future. You pretty much live inside a transport ship and you spend your time traversing space to different worlds in which you can attain and perform work gigs. There's no fucking way the time (and even the passing of time) will be the same on each world. Terraforming is a pretty cool feat of this future, but I don't think they were able to or cared to form a centralized system of time in which all planets and moons participate.
Okay, I'm starting to ramble a bit too much. My point is, how do you choose which time(zone) to abide by while floating through space when in reality space is your home? And can you imagine the awful amount of jetlag that you would get all the time? Or would you stop having an internal clock all together?
Tell me your thoughts and theories in the comments!