Just found the answer to the question I asked earlier in this thread (comment #629330 - 04/23/19 06:53 PM) asking about the specs for rotary dialing.

I found a BSP document 975-110-100 "Customer Loop Signals and Signaling Systems" (Jan 1980) that mentions the spec for dialing:

[Linked Image from seriss.com]

In particular the specifics of rotary speed and make/break pulses, which says the rate of pulses is 10 per second, with a between 58% and 64% break ratio (how long to break vs. make). Basically, a slightly longer open time than closed during pulsing. So if you do the simple math, if a complete pulse (on+off) must happen in a 100ms (1/10th of a second), the contacts need to be open between 58ms and 64ms during that 100ms.

The timing of old uncalibrated dials might be off that spec by a bit, so if someone wants to read old equipment, one should be pretty forgiving.

In the end, the technique I ended up using was so forgiving you could very carelessly flash the switchhook by hand, and still accurately dial without problems, so I didn't really have to pay much heed to the spec. But it is good to know what the spec is and see it in a document that is appropriate to define it.

I know the inter-office signalling was much faster; I recall dialing long distance back in the 80's and you could hear the fast inter-office dial pulsing during the connection process, which I'm sure Evan Doorbell has a million recordings of..!