The guy in the studio who appears to be here all the time, clearly working, has less to show for it than anyone else. Something just isn't working for him.
I've seen that happen a few times with people. Usually it comes down to confidence and just getting it right first time. Nervous, often new, animators can dive straight into a scene, work like blazes, then they find a snag. That snag causes them to rethink, change or dump what they've done already and try a different approach.
And then they find another snag. And it goes on.
Making changes to scenes in the good ol' days required more work, in theory. You'd have to dump bunches of pages and redraw from scratch. A whole new animation. With Flash, which we're working with now, you can modify things easier. You don't have to dump everything. You can go in and change symbols and amend timing seemingly with ease.
The problem is that, when you make quite a few changes, your Flash file can get really messy. Too many symbol changes, too many joins, pieces of animation that don't fit with others. It soon begins to show. Then the director doesn't approve the scene and it requires even more changes.
Sometimes it's better just to throw them out and start again, like the old days.
But in terms of working approach, this is not how most animators work anyway. They don't dive into a scene without knowing what they are doing. They look at it, feel it, figure out how it should work, look at what comes before and after and then, when they know what they're doing, they animate it. And, mostly, they get it right first time.
I suspect that's what the overnight guy isn't doing.