How do you get kittens used to humans and not hiss or be frightened of you?

I just got three feral kittens from my aunts farm. I understand that they would be a little shaken up from changing habitats, but is there anything I can do that will make the transition easier? I have done research and everything tells me the "time" will help. I am hoping that works, but I have a feeling it won't because of where they come from. They eat and drink water, but after a day I have yet to find either of them use the bathroom. Should I leave them be for a day and let them explore my room? or should I try to interact with them as much as possible?