Hi amamama,
We were told when we enrolled our children in the program that it takes 4 to 10 years to because academically fluent in a second language.
Is this for non-GT kids starting from Zero?
My wife is bilingual due to a similar program when she was in gradeschool - K through 5. I had two years in 7-8 Grade and speak other languages. Our nanny (Mrs E ) is 100% Spanish ( no exceptions) around kids. All of her former families' kids are 100% bilingual. DW can understand Mrs E 100% now and I am catching up to where I can understand some jokes.
It will help if you can find a babysitter who speaks it or if you can try. One tactic I used when learning other languages is to alternate language days. One day is English, the next is the target language.
As for reading English - who cares. I can put texts of each language side by side and go from one to the other and back. Or add in two more. It makes no difference.
The HARDEST thing for me around Spanish speakers, esp women, is they speak TOO FAST!!!!!