seed/seedling questions

hey everyone, I'm a first-time grower and I have a few questions:

1. I'm germinating five white widow seeds in cut up 2L coke bottles...while I was away for thanksgiving, two seeds' taproots pushed the seedlings out of the soil. Now the question: is this common and should I be concerned about the stress this might cause them? they were green when I got back, so I'm assuming they're still healthy, and I recovered them with half an inch of loose soil.

2. I'm getting a 400 watt hps system tomorow. How long should I keep using the fluros before I switch over?

Thanks
007

give it 2-3 week's then put them under the HPS ,but when you do start with the HPS as high as possible and work your way lower everyday untill thay reach the desiered hight.