This combined creates the following effects:
1) People spend the "dull" hours of the weekend gathering (ie: mornings). This creates a huge surge of supply while demand remains the same or even slows down a bit. This causes a sharp drop in prices starting friday evening, with subsequent hits on saturday and sunday evening.
2) During the week supply dies down while demand stays constant because lots of people will craft during the week (little time and not many heavy duty content being done). This causes a gradual increase in prices over the week, peaking on Thursday evening.