TBMC

Unpack right away. Take the plant out of the box the day it arrives and brush off packing material. A plant that arrives cool, wrinkled or light is fine — it is just thirsty. Soft is a different thing: soft flesh means rot, and that is what the 48-hour guarantee is for.

Pot it up. Use a fast-draining mix — roughly two parts gritty mineral to one part cactus soil. Pumice is the best of the mineral part and perlite works. Pot into dry or barely damp mix, never wet, and no deeper than it needs. If it wobbles, stake it: burying more of a plant is not safer, it is the commonest way to lose one.

Watering a rooted plant. A plant that arrives with roots is not on the cutting schedule. Pot it into dry, fast-draining mix at the depth it grew, and give it four or five days before the first water, so any root bruised in the box can heal. After that, water it the way you would any established cactus: soak the whole pot, let it dry out, soak it again, testing with a finger a couple of knuckles down rather than going by the calendar. Never leave a pot standing in a saucer.

Light. Bright light, but ease into full sun. It has just spent a few days in a dark box, so give it shade with plenty of ambient light for a few days, then half sun, then full. Going from shade to hard sun in the space of a week is enough to scar a plant permanently.