I personally believe that lower dose, longer length DNP cycles are better, more efficient and safer. The problem is, even on lower doses, many people have discomfort and lack energy.
Also, something to consider, is that working out while on DNP (especially at higher doeses) won't really help you build muscle... as muscle cannot really grow in a state that DNP creates. I have authority for this... of course.

... the point being that a shorter cycle will take you out of the gym for less time than a longer cycle. Granted, the lower dose cycle may not inhibit total muscle growth, but it will inhibit it.
Also, don't think for one second that you'll keep all your muscle while on DNP... while it is probably the most muscle sparing fat burner, it will still cause muscle loss.
I don't know how I got into all this based on the question of length and dosage of cycle... but I did...
C-ditty