Nearly 20 years ago I was in a management paper and learned that workers exist on a continuum between the consistent 9-5er and the inconsistent burst worker. It is no surprise that creatives are burst workers. A person whose natural tendency is to work in bursts but who has learned to fit into the 9-5 paradigm will have significant swings in productivity and motivation during the workday. It's almost axiomatic that the more creative a person the less consistent they are.
Designers rise to the challenge of completing deadlines but can become easily exhausted. Much of our training of designers instils into them the primacy of the deadline above all else and this reinforces the burst personality. For the industry this is helpful in that it helps "get projects out the door" and the downtime is necessary for rest, recovery and reflection. The danger is that overwork is much more difficult to detect and burnout is a real risk.
Burst work is fine when project are of generally short duration (i.e. not months or years) and deadlines are not daily. But as our deadlines extend (larger projects particularly web and development) then burst working is less desirable. IT has the "deathmarch project" where the deadline is far away but everybody is pushed into overwork to make it and larger design projects carry the same risks.
My own experience is that there are very few designers who find the consistency of 9-5 easy who are also great visual creatives. The consistent 9-5ers are normally competent and reliable but lack that creative spark or flair. They may be great technically and/or quite good visually but they're likely never going to win a creative award.
Don't knock them because their consistent workers are an important part of a design team. Not only do they handle the routine jobs more accurately and with less frustration, they also provide a yardstick of "normalcy" to their peers. They remind people that families are waiting, the sun goes up and down and the tides go in and out. They are living examples that despite our obsessive tendencies towards our projects and deadlines that there are more important things.
Burst work could be why we place so much emphasis on professionalism - particularly punctuality and attendance. Just to try and counter-act the tendency towards relying on burst work instead of proper planning. Perhaps this is the Confucian balance to the natural tendency of designers. The Confucian education principle here is that education often involves strategies for handling imbalanced tendencies. "Be more aggressive" a passive person and "Be more passive" to an aggressive person. In this aspect design is pragmatic: we need to work together at overlapping times in a team and we should do that when our clients are active (i.e. the working day). It helps our socialisation to even loosely fit a working pattern common in our culture.
There is a danger: if we do successfully turn these normally naturally burst workers into consistent 9-5ers then we may kill what it is that gives them the creative spark. Mindless consistency is the enemy of creativity. Therefore a mixed burst-consistent approach might provide a compromise; the creative bursters are allowed an equivalent but more irregular schedule provided they meet deadlines.
This is just another of those things that makes design hard: the right amounts of consistency and burst, unbounded creativity and creative pragmatism, obssessiveness but with perspective maintained. And this provides important decisions for employers building a team: it's often not just about the skill set, but how their work-style fits the work you do.