Before a player untaps their permanents during the untap step, the game checks to see if the day/night designation should change
If there is to be an extra item, such as a Gift Set or other collectors' items, as has been the case with many of the previous sets, it has not been officially announced yet, as of the time of writing
Even if this spell gets countered you still get four cards with it, likely providing you with future answers
Its drawback may look like its very punishing and can allow the opponent to surprise you via a mid-combat spell, but I never really saw that scenario play out since its damage prevention ability is a a conditional static ability so as long as its on when damage is dealt, it wont be prevented. (Thank you, @fenaris!) It usually plays out somewhat like a colorless Ashenmoor Gouger / Chimeric Idol where you typically dont bother trying to block with it (why am I blocking with my aggro guys anyway?) and, if need be, you cast a spell pre-combat to activate it (typically I used a large coin, like a quarter, to denote whether it was on or off)