Yellowing fan leaves...early flowering

I have read over all posts concerning yellowing fan leaves and have found none that match my situation.

I have 2 NL plants (buydutchseeds.com) doing well and are 3 weeks into flowering. The Fan leaves have begun to turn yellow starting from the bottom up. This has been gradual for about a week. I understand that this is typical of an aging plant but seems a bit early since I have about 4-5 weeks left before harvest.

I transplanted the plant that was more yellow to see if it was a rootbinding problem.

The set up:
- 400w MH for veg and now using HPS.
- Watering every couple days as needed with neuts about every
other watering and 1/2 to 1/4 strength
- one plant in 2 gallon bucket drains well
- one plant in 3.5 gallon bucket drains well (experiment to see if rootbound)
- Temp 82 and 67, day night respectivly
- Last PH measurement was 6.2 - 6.5 (4 days ago)

The questions:
1) Is this typical of life cycle? Do I need to worry?
2) Could these symptoms be from root binding?
3) Do I need to take further actions? If so, which?

The following symptoms may be observed if you allow your plants to become root-bound:

1. Stunted Growth.
2. Stretching.
3. Smaller and slower bud production.
4. Needs watering too often.
5. Easy to burn with low % nutrient solution mixtures.
6. Wilting.

Normal for fan leaves. No need to worry.

Thanks for the reassurance mogie! Do you think the plants are on track?

Well, you say you're growing NL. So maybe thats normal. NL only takes 6 weeks or so, right? Means yur half way through or just about. Everything is ok, don't panic.

Nl does finish early,well tha brand you have is supposed to.i had some from bds and they were monsters ,done in 7-8 wks

whens the last time she had any nitrogen?