Hatched many cuttles from eggs found on shore of south coast (Eastbourne, mostly) - eggs travelled home in damp seaweed. Never worried about temperature - some lived with tropical seahorses @ 80F (+?) upstairs in semi-natural tank (with reverse-flow filtration and protein skimmer, caulerpa weed) - temperature probably more important as they grow? Others hatched outdoors with native weeds (while I was hunting replacement eggs on a hot August day!), kept some unheated in the garage with a protein skimmer (vital to reduce waste and clean ink out of water) for over a year.
Vital that they can feed early (I only had access to "river shrimp"), which needs to be small enough that they can be caught, killed and eaten without the cuttle being kicked off. Non-feeders die. Later dead food (thawed shrimp, fish) may be taken but felt that fish might be worse if the cuttles have rear-end damage from hitting the glass. They learn that YOU feed them! I thought brine shrimp too "fluffy", only used in emergency. At least 1 cuttle developed a taste for young seahorses . . .