bleaching denim?

[linda-mah.livejournal.com]

i have 2 pairs of jeans a tub of bleach and water as i write this. i know leaving them in too long is good for the fabric, but i'm not sure how long to leave them in for. i am going to be dyeing them afterwards, so they don't need to be super-white, but they need to be able to take color. i know when you apply bleach directly to fabric it works instantly, but they've been in for about 10 minutes now and there is no drastic change. thanks!