Oh....she's only six, I can't imagine how behind she could be, they are only getting started at that age.
The early hours do seem a bit excessive, you don't want to turn her against learning.
Kids need their sleep to do well at school.
At the same time, you do hear about the rigorous schedules of Chinese kids and what they're able to accomplish.
I'd examine my motives to see if I was on the right track with her.
Is she really behind or are you afraid that she's behind?
Was she concerned or did she ask for help?
Could you be overdoing it because of your JW experience with education?
Are her accomplishments directly tied to your feelings of worth as a parent?
You can teach kids casually in non structured sessions and include the 3 year old. Teaching someone else is a good way to reaffirm what you know yourself.You could have the 6 year old teach the three year old what she knows and listen in.
I'd definitely get some professional advice and do some research. It would be easy for a well meaning parent to go overboard.