It's based on how far you are away from the home point. For the Avata, when the battery percentages starts to get low, I head back closer to home so I don't trigger the countdown because when it happens and it gets to zero, the drone will freeze...
Flickering Screens are never a good sign! The controller needs service or get a new one. You could open it up and dig around if you are so inclined you may just find a loose connection but its a crapshoot really.