^^Except most all Bosch relays already have diodes internally^^
Here's a question, tho, Dave........if a relay has no internal diode, and you add an external one, can a diode in series with a resistor increase release delay time?
Resistor adds loss, decrease time delay. Diode provides path for stored coil current to circulate, hence holding relay closed longer. A relay hold current is typically 1/4 normal operating current.
A scope can be used to capture hold time, by triggering key switch falling signal, and viewing relay output.