Do relays and solenoids, operate slower with a back emf diode? Yes!
On release of the switch the transistor powering the relay switches off, at the same time the second transistor starts the timer. The timer is then stopped when the normally closed contact of the relay relaxes into the closed position.
We did about fortyfive runs without, and about fortyfive with, the diode. The results are as follows:-
The relay magnetic field collapse is slowed significantly by the diode.