Late reply, but I'm 100% sure, from the moment they came out, the boxes said they would be unavailable to open on the 24th.
Besides, it's been years you've been playing this game, and Nexon hasn't changed. When they something is going to end, without some sort of severe glitch preventing it's use, it will end. Something lasting through/till the 23rd, means the 23rd is the last day. The only exception is when they say "till", and actually mean that the "moment it hits 12:00 AM PST." Which is a rare scenario these days, thankfully.