In our case there was no SOP regarding the timing of the use of disc per se; different pilots did it different ways, as did different instructors. Most did not wait for the nose to come down. Personal experience and a few thousand hours in the airplane later, it seems like the guys who put the nose down before starting to use Disc had faster and longer landing rollouts (for obvious reasons). This was always uncomfortable on some short runways and resulted in the one and only time in my career that I've ever had to physically take an aircraft from someone who was not a student.
Have never heard of anyone losing an engine in the Dash during that part of landing (not that it hasn't happened), and if the prop overspeeds in Disc one would imagine the nose would come down immediately whether you wanted it too or not. In assessing the comparative risks I'd go with the technique mentioned in the previous post, personally. Barring something limiting in the type's AFM / FCOM, it comes down to SOPs and technique, in that order.