Ordering from Apple store question

Wasn't sure where this question should go but

AirPods don't look to be in stock until next month (bummer, but that's fine). I was going to just buy now, but my question is - do they charge your card right away, or only when it's prepping for shipment / shipping? Not a big deal, but I'd rather not have a almost $170 charge on my card for a month without the actual product.