The idea was to not make it dependent on the DATEFIRST setting and the basis there was no calendar table. Using DATEDIFF(DAY,0,@StartDate)%7 you know that 0 will always be the Monday. Rather than generating all the dates from the range and then filtering it down, was just playing around with finding the first of the required days in the range then adding the multiples of 7 to get the subsequent days.

As I said boredom and a bit of fun!