Arriving at the entrance by 6 in the morning means that it would also be extremely cold – after all, you'll be standing further up above sea level minus sunshine, so this is to be expected. Keep in mind, or better yet, place a reminder on your smart device, so that you wouldn't leave your sweater or jersey back at your room in your hotel. Nevertheless, as the sun slowly rises above the plains, you will feel warm and wouldn't need the extra layers after all. Although the hike in Horton Plains isn't much of a challenge, it is advisable to wear comfortable hiking boots, or even your sneakers – just don't wear flip flops! Bring your hat and sunscreen to avoid getting a sunburn by noon.