Cats are fairly low maintenance animals. As kittens, they love to play and interact A LOT more then when they grow up. Cats can mostly preoccupy themselves and, depending on the cat, are fairly aloof and self-maintained. This of course is not ALL cats. When I was young, my house cats were fairly low maintenance. If they wanted pets, they came and jumped on your lap. Once they were done, they would leave. These were also indoor outdoor cats so they had other things to preoccupy their lives with either then human interaction. They did not seek out human interaction a whole lot (making them actually quite boring for my 6 yr self who just wanted to cuddle and cuddle and CUDDLE lol).
The only fully indoor cat I've ever had has been my current 9 yr old torti Meenu, and she is VERY interactive. She will follow me everywhere (even the washroom), answer me with a meow every time I say something, sleep with me and my fiance, she plays fetch for heavens sake! So I end up interacting with her a lot ( and I absolutely adore every minute of it, so does she). The amount of one on one time your cat will require depends largely upon the cat's natural personality. I think you'll find that once you get your cat, too much time is undefinable, because you will want to spend lots of time with him/her, it never feels like a burden having to take care of a cat!
In terms of upkeep - low maintenance. You scoop out the litter box once or twice a day. Feed and clean the water dish about twice or three times a day (with a kitten maybe a bit more) and, well, thats a about it for daily tasks! Give them a brush session once a week (Meenu LOVES to be brushed so I do it a few more times a week) and clip the nails when they get sharp.