RHS site says it flowers in summer - so August/September would seem reasonable given the slow start to this year's growing season with most things being late flowering.

Does it appear to be setting any fruit?

http://www.scotplantsdirect.co.uk/planting-care/soft-fruit/goji-berries/prod_359.html might prove helpful.

thank you for your reply just come back off my holidays 15th sept 2013 still flowering can't see any berries starting to form yet though but ive never seen as many flowers. thanks sam.