They are posted out by the school not directly from the examiners so it's entirely down to when they are able to/choose to do it, whether they post 1st or 2nd class and how good the postal service is in your area. If they don't have many to do and you have already provided them with a 1st class stamped envelope with your address then they might prepare them when they receive the results on Wednesday to make the Thursday post and be with you on Friday. Exams staff will have a lot of stuff to sort out for results day, analysing results for the school leadership team, preparing the results for students and then processing enquiries about results, remark requests, copies of script requests from candidates etc and so may may not be able to prioritise posting your results. It could just as easily be Monday or later when you get them. Your exams officer will be able to give you an idea of the likely timescales for your school.