is it okay to leave a kitten home alone for 6-7 hours a day?

As long as the kitten is house-broken, has several clean litter trays and water/biscuits, she should be fine. Cats, and kittens, spend the majority of their times sleeping. Our cats are often left alone for 6 hours or so while I'm at school and the rest are work and they manage fine. Maybe leave some toys lying around so your kitten can play with them if she gets bored.

Cats do not need the supervision that dogs do.
If litter box is clean and food and water is available for her she will sleep the day away..

Kittens spend a lot of time sleeping so yes.

yes, many people do it. Cats are pretty independent.