The ship do need travel at lets at warp 3.5 doing the knight when it notOrbiting a Planet.
I do like the way you've arranged the crew though, if they were using a three shift cycle.
The way I see it, there's 4, 6 hour shifts, that work like this. I'll be using the "Alpha shift" crew as an example:
The first 6 hour shift, from, say, 0600- 1200 hrs, would be "Alpha shift". All the senior staff would work this shift (bridge crew, etc), at their posts, so on the bridge, in engineering, whatever. The next 6 hour shift, "Beta Shift", those who were on duty for Alpha would still remain "on call", if you will. They don't have to be at their stations, but they would be doing something related to their job, so, T'Pol could be supervising the science labs, and Malcolm would be fooling with his precious torpedoes. The next two shifts, from 1800-0600, Alpha shift crew would be off duty, sleeping, or doing what they please.
Now, each crew member wouldn't necessarily follow this pattern, but they'd be working one 6 hour duty shift, one 6 hour period of "light duty", and two 6 hour shifts off. So, it could go duty-off-light duty-off, oir any combination of the four. This would allow for there to be no set number of crew on any shift (I'd imagine though, that Alpha and Beta would still be the most heavily staffed.) This allows you to space out a limited crew. There could be say, 20 scientists on alpha shift, and of those 20, 10 would serve their light duty on Beta shift, and the other 10 on the third shift.
I hope this makes some sense, but if it doesn't, let me know and I'll try to flesh out my thoughts a bit better.