From experience and DH was convenienced about the early handling/socialization. We lived on a farm. Before we married, DH had several litters of kittens. The kittens were never brought inside till they were about 7-8 weeks old for training and they were hard to catch in the barn.
The last litter (Ling's brothers/sisters); the kittens were confined in a very large dog crate and brought in by 5 weeks old to wean/train.
They stayed around for 3-4 months old (normally DH would give the kittens away as soon as they were eating/using the litter pan). He found out the importance of how to take care of kittens the right way and socialize them. This last litter was totally different and much friendlier then any of his other litters.
And even tho the kits will know you by sound/smell, don't be surprised if they still "hiss" at you for the first week or so when eyes are open - its natural instinct