If it were really putting out 1200 lumens, less than an hour would be my guess. But they don't really put out that many lumens, that rating is the max for a single lamp cell and a 18650 can't supply that much power. You get more like 600 lumens, still plenty of light, and it'll last just over an hour on high. I run mine in strobe mode and it lasts a lot longer but I don't know how much as I've never let it run completely down from the full charge. I've only been using it a few months, and it is only now getting dark early enough that I'm likely to ride in the dark the entire way home. I used mine on the way into work for about 10 minutes and on the way home for an hour yesterday and it was still going strong.

Keep in mind too that these batteries take a long time to charge, something like 5-6 hours on the charger that's included.

I also have a Lezyne Super Drive and the funny thing is that I've hardly used it at all, but it is also a nice light. It is better made than my flashlight, and has a USB charger built in. It may be worth it at the discounted price, but I wouldn't pay full price for it as it isn't worth 4x the price of a flashlight. The reason I don't use it is that the bike I used it on went away to college with my son. He didn't think he'd need anything like that to ride around campus, and I still wanted to use it myself.

I feel a lot more visible at night now than during the day. Nobody dares cross in front of me because they think there's a freight train approaching, not a bike!