I believe that this achievement is now glitched. I just started playing it recently and have been unable to get this achievement.
When the game was originally released, it did not have the slo-mo's. So as explained in the achievement guide, you could plug your phone into the charger and let it play itself for an hour straight, netting the achievement.
Now that the slo-mo's have been added (in an update at the beginning of January), the game automatically pauses itself after so many deaths, asking if you want to use a slo-mo. This makes the achievement impossible.
It'd be great if there was a fix for this, but I'm not holding my breath.