How many hours in a day?
You've seen the title, and you're probably wondering what the catch is. You don't write a full paragraph (or more) about the good news that yes, in fact, there really are only 24 hours in a day. So what gives? Well, since you asked...
Say that on your birthday, you just happened to be in New Zealand at midnight. The timezone is UTC+13, thanks to daylight savings time. You hop on a plane, and fly to American Samoa the long way around – first passing over Australia, then Africa and South America, before finally landing at Pago Pago International Airport at 23:59. It's still your birthday, but now in the timezone UTC-11.
All up, your flight was 48 hours long – and so was your birthday!
Speaking of which, have you ever gotten annoying happy birthday emails from companies trying to sell you shit the day before or after your birthday? It's probably because they don't know what timezone you're in. So here's a neat little trick: just do a round-the-world trip from New Zealand to American Samoa on your birthday! Now the emails will always arrive on time! Problem solved.