All U.S. East Coast posters will want to set GMT -4 during the summer (to compensate for daylight savings time) and GMT -5 during the offseason.

U.K. posters will all want flat GMT.  I don't know if we have any visitors from any other time zones yet, but I'll be happy to help anyone who needs it.

System time is set to GMT -4 (aka Nats time)