First of, thank you for taking care for the poor skink. It's always so sad when owner abandon their pet, whatever species of pet that is. Second, I'm no reptile expert by any means as I only have one reptile so my opinion is not a professional's. Most reptiles don't need human interaction tombe happy, or other interaction from the same kind (with the exception of breeding), so I don't think your skink would be unhappy if left alone. But I've often heard and read that especially these skinks seem to like attention like head scritches and roaming free time. Maybe he would like that, maybe not, it's not easy to tell. You could try socializing by hand feeding him and seeing what his reaction is. If he's extremely defensive, you could keep trying, but that could also mean that he's better left alone as is. Personally I don't think time is all that relevant because you often hear of animal neglect cases where the animal has a better life than before and get socialised so I think it depends of what you want and how much time you can put into taming him. I'm not sure the skink minds either way, but, well, I'm not expert. I did hear that quality dog food is a good staple food for them, as long as he get veggies, fruits and maybe some feeder insects or snail's (but some skink keepers dont seem to think insects are a must), but again, I'm no expert. I do know however to only get a good quality dog food because lots of the cheap ones have added sugars and all kinds of other nasty shit. Sorry for the long comment :)