You shouldn't have to wait two weeks to get the sort of information you're seeking. It should be available on the school's own website. If it's not, you should complain to the school.
Examination timetables are available online, here:
http://www.modernisationonline.org.uk/comptime table/
The rules for determining the school leaving date are set down in DfES circular 11/97. This states that the relevant date is the last Friday in June. i.e. 29/06/07
http://www.dfes.gov.uk/publications/guidanceon thelaw/11_97/intro.htm#top
Arrangements for work experience are either made by individual schools or by the relevant local education authority. If the dates fall within the normal school calendar (i.e. before the leaving date), work experience forms part of the school's curriculum and is therefore compulsory. However, it's extremely unlikely that any LEA would prosecute the parents of any young person for non-attendance during this period if it occurs after the GCSE exams.
Chris