Help with the international date line?

There is something wrong, if you're leaving on the 27th at noon it's already 3:00 AM in Bangkok on the 28th, so there's no way you're going to arrive in Bangkok at 12:30 AM on the 28th. It probably is 12:30 AM on the 29th when you arrive, but you better check with your airline to be sure. You can always get a taxi from the taxi stand right outside the area called the Meeting Point. Use the taxi stand and the metered taxis there and avoid the touts that mill around the Meeting Point. The fare should be around 300 baht inc. a 50 baht airport surcharge and tollway fees and is probably the best way to get into the city anyhow, most hotels will charge much more than that. There's also a hotel reservation desk near Meeting Area C where you'll likely exit the customs area on the opposite end of the terminal from the Meeting Point if you don't already have a reservation.