My simple test to see if a pto shaft needs cutting AT ALL - mount the implement, hook up the pto shaft, then, while watching the two telescoping shield sections, (PTO NOT TURNING) raise and lower the implement looking for the most engagement between halves (shortest overall length) - stop the lift at that position, turn off the tractor, and try to remove one end of the shaft.
If you can do this without "bottoming" the two halves, you're DONE. If not, you will probably need to watch the video or RTFM, etc.
Keep in mind that, if you later decide to put a quick hitch on your tractor (bought more implements, imagine that :=) you will be moving the implements further away from the tractor by about 4-6 inches - so if you cut your shaft UN-NECESSARILY, you may need to buy a NEW shaft in order to add a quick hitch. This will raise the cost of adding the QH by double or triple.
HTH... Steve
Oh, forgot to mention - if any of your implements is "ground engaging" (like a tiller) you may need to elevate the rear tires enough (ramps, whatever) so your tiller will go as low relative to the tractor as it will be when it's in the ground - I've never seen this to be true, but it could happen if the shortest shaft length occurs somewhere OTHER than mid-range of the lift.
Also, don't forget that your TOPLINK needs to be at the adjustment point it will be used at during the above test - it will also affect pto shaft distance between ends.