Pull-time on first wingsuit BASE jump
So, I'm used to the visuals at pull-time on a regular terminal BASE jump. The way I got there, I suppose, was that I went to some big walls where someone told me, "It's x seconds to impact, but if you aren't tumbling like an idiot you should be able to take at least y seconds." On the first jump, I counted to y and had a good look at the ground coming up. Next time, I counted to y and then waited a couple seconds more before pitching. And so on. However, one thing I've heard fairly consistently about wingsuit BASE is, "Don't wait for the familiar feeling of groundrush, because if you usually pull at 300 feet, you'll be pulling around 100 feet with a wingsuit."
I'm getting set to do my first wingsuit BASE jump from a 1200-foot wall with about 2000 feet of high-angle talus below that. I've done a couple of jumps from this one before, but I haven't got any reliable accounts of wingsuit flights from here. So I have no one who can tell me, "Try 30 seconds for starters, then work your way up from there." What I'm wondering is, how should I judge pull-time? If groundrush is out, then I'm thinking either (a) I could use a conservative count based on the altitude available to me or (b) I could use some kind of visual reference on the opposite side of the valley.
I'd like to hear any pointers on how to judge altitude the first few jumps, and also maybe any first-hand accounts of first wingsuit BASE jumps which might give me an idea what to expect. Thanks!
Michael