Had you mentioned it at the interview I think they would have honoured the holiday. However, Now they may not, It depends what kind of people they are really, However, They may be OK and allow you the holiday or allow you to take the time off unpaid, Or maybe they will say you have to find people willing to cover your shifts and you pay them back at a later date. Ring and see asap. They should have asked you at the interview really but then again, You should have said. As i said, if they don't honour it, You can probably find people willing to cover your shifts assuming this is possible or ask for it off unpaid, Not ideal i know but you'll have 8 weeks to put a bit aside to cover the loss of wages. Good luck and happy hols.