The bolt delay setting has more to do with eye timing than with solenoid timing, and so the operation of the marker does not impact on this setting or the necessity to get the value of the setting in the right ball park.
Basically, in order for the eye system to work correctly, the eye needs to be able to differentiate between looking at the bolt and looking at the ball. The eye first wants to see the bolt retract, then to see an empty breech, then to see a ball enter the breech. That way it knows that the last cycle has ended, and that a new ball has loaded and the marker is ready to fire again.
If the bolt delay is not set correctly- for instance, if it were too short - the eye would expect the bolt to retract quicker than it could, would look for an empty breech too soon, and when the breech was not seen to be empty (because the eye was still seeing the bolt, only partly retracted), the board would think that the eyes were damaged or covered in paint and register an eye fault.
So, irrespective of how the marker actually cycles the bolt, there is still a delay between the marker firing, the bolt retracting, and the eye seeing an empty breech. The board still needs to be told when the eye should start looking for an empty breech.