This achievement is ridiculously easy.
You don't even have to have the game running actively on your X1, as long as it's running and it's on the pause screen you can use your X1 to watch Twitch, TV or even the WWE Network. As long as the game is in quick resume it seems to count that as time on the planet. I don't know how long that'll stay around for or if they'll even patch it.
Personally I paused the game and was in the middle of watching something on the WWE network and this popped halfway through the show I was watching.
DO NOT OPEN ANOTHER GAME - I'm guessing that it can only be an App though as if you open another game it would take Lifeless Planet out of the quick resume status and replaces it with the new one.
TECHNICAL REASON -
(Many of you probably already know this) The Xbox1 technically runs 3 operating systems although Wikipedia says it's only 2 and the top layer doesn't count as an O/S.
A top layer that runs the virtual layer, a virtual O/S that runs the games, and one that runs the User Interface and Apps. As long as the game is in the Virtual O/S then time is passing according to the game. This is bad programming on the part of the Dev. If your X1 is in standby or Quick Resume mode then time is also passing so should add to that total as well. Opening a different game would remove it from that layer which is why opening another game is bad.
Having said that though "FullMoonBeaver" (great name by the way) has said that he opened up Minecraft and it popped for him but he had been using other apps etc.
From TheIcemanCometh (I cannot verify this though, the solution that is) -
I'm not sure this works any more. I started the game last night, played long enough to get the high-fall death and 15 minutes in town achievements. Also decided to try this method overnight. My XB1X is set to turn off after six hours of inactivity, but I was up before that kicked in. I would have figured I would be at about 70% complete by then, but I was only at 34%. I had the game running in the background (game showed Resume on the dashboard). Not going to -1 this solution, but wanted to pass on the information nonetheless.