Oh, I like the way you think - just, maybe let the "little grey cells" have a lie down for a bit! And a bun. Buns are good.
I agree with your thoughts on Void Field mining. (My first thought when that popped up was to look out for Void Cows. Ahem)
The passage of time is a Thing, and having a set finish time, regardless of when you start does feel a bit weird, as well as compressing the time available for one's evening rounds attending to the crew's needs, visiting the Space Bar (I note that there's no lock requiring an Any Key) and so on. You could say the same thing about T'Ris and her station walks. After the first one for each outfit it takes her all blinking day, rather than an hour, maybe two. What's she doing?
Have a set period, maybe a late start penalty as you said, and the rest is gravy. Or custard.