Problem: How do you divide all Mendel parts into 5 sets of equal print time and bed size? The goal is to have 5 twelve hour print jobs that can be started in the morning and evening.
Complicated Solution: In Computer Science this problem would be classified as a knapsack problem, with print time and bed size equally playing into the "cost" of each item. I more than considered coding one of the knapsack solutions and running it on part data before stepping away.
Simple Solution: Assume that a long print time is always equal to a large bed size with each part. Create a list of parts with name and print time. Order the list by print time. Treat the parts like people and ask them to count off in order from 1 to 5. Group all 1s together for your first set. Group all 2s together for your second set and so on.
The simple solution can be carried out in a spreadsheet in less than a minute, and it gives sets that would take between 11 and 13 hours to print, according to data from reprap.org. It's then only a matter of tweaking the sets by taking a larger part from one of the larger sets and swapping it for a smaller part from a smaller set. I did this a few times until I had 5 sets that should each take almost exactly 12 hours to print.
Here are some images of the first set.
In the next few weeks I will add this series of STLs to Thingiverse.