Its done when there is no more change, and no chlorine coming off. You can't overcook it.
My kathode turns black on top. Do you think it's losing a gold?
My K also is black along the water-line (image 4 above) and I wondered @ chlorine-copper-zinc - chlorides due to the chlorine? (K is brass sheet.) AFAI can see no Au plates onto K but waiting on 10mg FSD scale to measure ingot-loss as current one faulty.
It's not a deposit, more like a plated effect.
Also after 3 runs there was a black deposit on the gold ingot alligator-clip that could be scraped-off but nothing in the liquid. (The alligator clip gets evaporated liquid, it's not in electrolyte.)
Looking for some thin silicone tube to sort-of 'condomise' the junction.
So far batches seem ok, very clear, darkish ruby-red and taste a bit cinnamon, no salt-taste. 500ml runs have been 20mins @ 350mA - one 30V, others 60V, ingredients as Kephra advised.
Seems the large K allows A movement anywhere within the liquid (not close to K) and current virtually unchanged. The 1mg ingot is only immersed @ 3mm.
tony