Dan Ariely’s ideas of Predictably Irrational claims that procrastination is a universally human issue. According to Ariely’s studies, people do better when they complete the work closer to the start of the project than if they leave it to the last minute.
Based on this idea he suggests that there are two things you can do to ensure delivery on or before the deadline arrives. The first is to set deadlines for competing the work long before the actual deadline. The second thing is to let the people doing the work set their own deadlines. The key issue with allowing the people doing the work to set deadlines is to tell them first about this concept. In other words, the fact that they are aware of this human behavior will make them set deadlines well be fore they are due.
In the design of websites this might translate to asking the designer doing the work to set their own deadlines. Could you even request that the deadline must be at least 50% before the actual deadline? How would this knowledge change the way you work with clients?