Some where every 800 - 1200 usually. You seem to have gotten rather unlucky, so I would wager that you'll probably get your 2nd on the lower end of that. My first was 1170, but my 2nd was 1080.

But it is possible you might get really unlucky and not get it till 2500. Just make sure you take advantage of doing 300 pulls. Those extra 66 seal make a big difference in the long run.