Thought Forex is traded all over the world. Still are some major trading centers. There are four standard sessions in forex market. London, New York, Tokyo, Sydney.
Wherever a market is, where exchange happens. Major trading transactions always happen in financial center, so I figure out the forex trading market sessions base on http://en.wikipedia.org/wiki/Financial_centre
Forex market is trading unstop 24 hours a day except weekends, i.e. trading from 20:15 GMT on Sunday until 22:00 GMT Friday.
Bank working hours 9:00am ~ 6:00pm.
Again, the broker server maybe in different timezone, so the time zone offset from the broker must be assure.