Centres may start examinations earlier than, or later than, the published starting time for the session without prior permission from Edexcel. However, in order to maintain the security of the examination. All candidates must start examinations scheduled for a morning session no earlier than 8.30 a.m. and by 9.30 a.m. and for an afternoon session no earlier than 1.00 p.m. and by 2.00 p.m. Source Link :- http://letmeget.com/blog/gcse-timetable-2010-gcse-exam-dates-2010