That could be your reason for not growing. Not knowing what tension you're at is never really good, but you should be extending for a minimum of 4 hours to get any real effects from it. The studies on extending show 4-6 hours is what you want to be at, even though some people extend for over 8 hours a day.
I agree with DemOne - it is essential to know what tension you are at. Somewhere between 600-1200 grams seems to be very efficient for most people)
Also, when I was extending (I've switched to hanging for a while), I was extending 10 hours per day - a single 6 hour session, a short break, then a 4 hour session. I saw .8" in 1500 hours extending this way - you may be on track as in my experience, and having talked to many others, .25" per 500 hours seems to be on track (despite what the 1"/1000 hours claims I've seen say).
Gains from extenders usually come when they want to come. I may be off on this, but people usually notice small spurts of growth every 250 or so hours. This is of course while using proper tension and time.
so did you get your gains after your 1000 hours or you saw gains every 500 hours??
I didn't really pay that much attention, other than to measure every month or so. The gains seemed fairly consistent, but I'm just working from memory here. Most of it is recorded in my blog if you want to check that out.