>>Since this technique depends on Randomization working as well with long 
>>Schedule Durations as with shorter, does anyone have experience with 
>>Durations of four hours or more? Did it go alright?

Do it all the time.  Whenever I set up a new customer, I tell them to make the 
Duration window as big as they can tolerate (usually 8-12 hours), throw all the 
clients in.  Then see what clients cause a problem, and make special schedules 
for the clients that need to be forced to more particular start/run times.