I help in a private cat/kitten rescue (cleaning litter trays feeding etc) we had an orphan litter of 5 five week olds come in via a 3rd party.
Day 0 or 1 they were all distrustful of us (owner and 2 helpers) probably due to no previous human contact. They were flea treated and wormed and put in a 3m long 1.5m deep and meter high cage in the lounge with a bed food and litter trays. Being in the lounge is policy for orphans. If they are so young they require bottle feeding the owner takes them to her bedroom at night.
Fast forward to day 3; 3/5 are happy to be picked up patted etc and the 4th dislikes being picked up (hisses) but as soon as you do it starts purring and shows signs of enjoying the attention. We added some toys to. The 5th hisses and growls. Two weeks later it no longer growls when you get near the cage but still exhibits a fear response. I've been feeding it in my lap for the last 3 days while slowly stroking it in an attempt at classical conditioning for positive association with me.
All kittens are handled by all of us through the day, obviously the 3 who ask to be picked up get more interaction but I make a point of handling the other 2 at least once while I'm there for 1-2 hours. I can't take it to my home and invest more time/effort in it
I have owned 3 cats (back to back) and Mum & I used to help my local (then) SPCA taking kittens home for as many weekends as necessary to socialise them ("mummy it likes me, it's purring") I am aware that some cats just co-exisit with a humans but I want to maximize its adoptibility. I'm in a city and it has a low play drive so a barn cats program isn't a viable solution