Does this mean your credit card will NOT be charged before you have ended your stay at the hotel? Or does it mean you will NOT be charged before 4 weeks prior to the convention? OR does it mean your credit card will be charged as soon as you make the reservation with the hotel itself?
It's explained in the posting you refer to. They won't charge you at the time of reservation. The card gets charged immediately when you cancel your reservation after the cancellation deadline. It will be charged after check out if you show up on time. You can provide a different credit card on check in, or even check out.
Blocking a certain amount on the card is a different aspect, though. They'll likely block a small amount (1 EUR or so) on reservation to verify that they can process the card. They'll block the full amount (maybe plus some some safety) at check in on the card presented. (Blocked amounts may appear as a charge on certain debit cards, it'll get refunded automatically if the hotel doesn't actually invoice it.)