The variability of the drip method based primarily on supply pressure is one of the principal reasons why the RIV method was developed.

For the later 617's, an electronic probe is inserted into the IP and the timing can be accurately set to within 1/2 degree, independent of fuel pressure and drip counts.

The entire discussion of drops per second is somewhat over the top when the variability of fuel pressure during the process is ignored. The drip method is a compromise, at best, and the accuracy is not better than +/- 1.5 degrees or so.