Just been out for another wander, this game uses about 1% a minute charge wise, which is pretty excessive
When you get to the leaves just wait if you want to. All that means is that the chance of one appearing is greatly increased, not that one will be there for certain. I've got a fair number of pokemon in non leaf areas when wandering around, so it is just luck.
It's really relaxing to play, take a stroll around with your phone in your hand, when there is a pokemon you can catch it vibrates, catch it, carry on walking. You only need to actually look at your phone if it vibrates.