The Global Clock Page. See below for common time zones to find out what time the trials start or what time it is for fellow guildies. 

ALL TRIAL TIMES ARE EST (EASTERN STANDARD TIME)

Eastern Standard Time (America)
Central European Time (Europe)
Beijing Time (China)
Australian Eastern Daylight Time (Australia)
Pacific Standard Time (America - West Coast)
New Zealand Daylight Time (New Zealand)
South Africa Standard Time (South Africa)
Brasilia Summer Time (Brazil)