For North America, the game servers are either located on the West Coast or the East Coast of the USA.
West Coast servers are based on PST, you can check the time here: https://time.is/PST
East Coast servers are based on EST, you can check the time here: https://time.is/EST
There is also a new non-PK server based on CST: https://time.is/CST
Keep in mind the servers are set on Standard Time, and as such the server time will not change even if your country follows the daylight saving scheme!