In Argentina, December 24th is not an official holiday, but as a custom, most administrative offices and public-facing businesses are closed, or they only open for half a day, meaning 4 hours. That's how it works here. My sister-in-law, who works in an accounting office, told me she’s never worked on this date. The same goes for December 31st, as many places close or have reduced hours. So don’t get your hopes up, it's likely that Western Union will also be closed. It’s best to plan ahead and make sure you have enough cash for the holidays.