I've frankly never heard of this but it sounds right to me. I'll be glad to hear peer comments.

First let's explain what it means: Whenever a certain event occurs (e.g. a switch closes, a device discharges etc.), the voltage deviates from its steady state level and then gradually recovers to a new steady state value. The time until this occurs is the transient time. The phenomenon itself is the voltage recovery. Your phrase most probably refers to the description of the momentary voltage level as a function of time.
Therefore:
hishtanut = change / variation
metach = voltage
hitosheshut = recovery (heh, tav, alef, vav, shin, shin, vav, tav)
betkufat hanavar - during the transient time / transition period.

I definitely can think of more concise formulations, but they are bound to be less clear.

(metach shiuv holef)
In this case I would prefer using "shiuv" as a more accorate transalation of "recovery", since it means "return to privious state".