I guess I was on a roll
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About selecting D2 , components tolerances vary from one to the next. With zeners the 'zener voltage' is the primary spec, like 13vdc +/- 5% tolerance, so a voltage from 12.35v to 13.65v would be in spec. You can try them in circuit, but that can be hard on the pcb with all the soldering and un-soldering. Or you can make a test jig with a resistor and a couple of 9v batteries and your meter (for any zener or pn junction):
Zeners are cheap, I bought 100 each of the common values used in Pioneer amps, so I can use a test jig to select from them.
The regulated voltage is proportional (but not linear, because of the gain in the regulator) to the differences in the reference zener voltages, so a slightly high one raises the regulated voltage, a slightly low one lowers it. You can 'tune' a voltage regulator that way, to some extent. The voltage in the jig will not exactly match the voltage in circuit unless you get exactly the same current through it, but again they track. If you measure D2 in the jig and then find one from your stock that is lower, it will be lower in circuit also. I may be may overthinking this but, it does work, I have done it before.
You can also select resistors in the feedback divider but that is much more work. This may be way more than you want to get in to.
If your lamps are all working they are 'unburned' On my SX-1050 the Speaker A lamp quit working many years ago (burned out) and the AUX lamp is also dead. When those switches are selected the load on the lamp circuit is reduced and the voltage rises, so the other lamps get brighter. I can see the voltage rise on pin 18 and 19 of the -103 pcb. The circuit is intended to have a minimum load no matter which switches are elected, IF all the bulbs are good.
If I select an input other than AUX and Speakers other than only A the minimum load is satisfied, the voltage is correct and the lamps all have equal and correct brightness.
Ripple Killer, often called a 'capacitor multiplier' is much like a voltage regulator.
The attached schematic has the 'voltage regulators' in blue boxes. Their reference voltage is the zener diode and their outputs are intended to have a constant dc voltage with low ripple, regulated down from a higher (less stable) dc voltage with much larger ripple. The circuits in green boxes are often called 'capacitor multipliers'. Their input is an already regulated voltage, their job is to kill ripple caused by a varying load. Their primary function is killing ripple without using a large expensive capacitor, and providing a stable lower dc voltage from a higher regulated voltage, rather than providing a regulated voltage from an independent reference like a zener diode. The two circuits are very similar, but not quite the same. The output dc voltage of the ripple killer is dependent on its input voltage, where the voltage regulator's dc output voltage is independent of its input voltage (unless its input drops too low).
End of lecture, hope that helped and was not too long winded . . .
Six seconds seems OK to me for the protection relay, that may change after the power supplies, dc offset and bias are set correctly, don't worry about it until then.
If you used Q9, 10 and 11 replacements recommended by MTF or one of the other long time techs current BOMs they should be fine, unless one is off a bit. The transistor whose emitter is connected to the zener is the one that (its gain) controls the regulator voltage primarily, it need to be a high gain fast transistor, the other (one or) two are there for current gain and power handling.
Hope that all helps rather than confuses. But don't hesitate to ask
I got carried away again.