I'm wondering how long it takes the Air in sleep mode to actually change into the 30-day sleep mode, where the battery can last a month. Does anyone know? It seems to me, whenever I open my Air after a night unplugged, whilst asleep, the battery percentage drops about 5% or so, if not a little more. If I do the math, that's 20 days-ish, give or take. How does this 30-day sleep thing actually work?