It actually took a bit more planning and figuring out then I would have expected.
I signed up for weight watchers on a Sunday so that was my original with in day. The problem with that is the last day of my WW week is Shabbos. Since I use all my extra points on that day it didn't seem so wise to get weighed the day after. So I changed my day to Monday. That didn't really seem to help. By week 3 I decided to weigh myself every day to see what would happen. Turns out I need till Tuesday to recover from Shabbos and then till Friday to actually lose weight.
So it's official. My new weigh in day is Friday.