In FileMaker-speak Saturday is day 7 (see FM Help: "The number 1 represents Sunday, 2 represents Monday, 3 represents Tuesday, and so on.") To localise your start date, adapt Phil's solution in the following current thread: Monday of the week
Apologies, 6 was a typo, I should have said 7. Let me checkout your answer.
That worked very nicely - thanks.