You can now earn double XP for taking part in different activities at specific times of the day. For example between 6am and 9am EST you will earn 2x XP for fishing up anything! Between 9am and 12pm you earn double XP for harvesting items like wood and metal!
For a full list of ways to earn double XP, open the MOTD in-game with the !motd command and hover your mouse over one of the bars at the top. This will show you what event is currently earning you double XP and how long until the next event starts!