Actually, I always thought it would make much more sense for First officer to take night shift, while Captain had day shift. That way, there was always a senior officer on the bridge, since emergency situations could come up at any time. Or perhaps there should have been 3 eight-hour shifts, led by the Capt., First Officer, and Second Officer.
I probably wouldn't want to put all my top guys on the bridge at once, except during an emergency situation.
Maybe you would if you're producing a TV-show and your actors want
screentime. 
But in general, I agree with you.
How did their shift-system work anyway? Is it only night and day, or is it 3/4-shifts-system?
Well, if it's anything like RL in the USCG or USN, then they're probably running a three 4-hour watch routine (i.e. 0800-1200, 1200-1600, 1600-2000, etc.).
It's typically referred to as '1-in-3', since you stand one watch in every three. This depends on the number of qualified watchstanders per position, of course. If you're lucky enough to be on a ship that has, say, 6 qualified OOD's (Officer of the Deck), then you (as a person) would only stand 1 watch per 24-hour day (1-in-6).
Note: Some ships or places will change/split the 1600-2000 watch into two "Dog" watches, typically 1600-1730 and 1730-2000, to account for both dinner and to throw some 'variety' into which watch you stand. Otherwise, like the poster mentioned above, you may always get "stuck" on the 0000-0400 (the "Mid" watch), and never be known to exist...
(By the end of one trip on the icebreaker, we had 11 qualified EOW's, so we were standing one 4-hour watch every day and a bit. It was actually pretty damn difficult on your biological clock, even though it was a nice rotation, weird as that sounds!)
Traditionally, the Navigator would take the 0400-0800 watch, during the age of celestial navigation, in order to 'shoot' the stars & planets and thus, figure out where the heck the ship was... In the same vein, the XO (Executive Officer) would take the 0800-1200 watch to kick off the daily routine. You don't see either case anymore or at least, rarely...
Cheers,
-CM-