I usually wait until Monday to start a new program, just so it’s easier to follow the calendar and I’m not confusing myself. However, if you are feeling motivated today! Maybe start the work outs, take a rest day on Sunday and then restart first day on Monday?
I would just start. It’s hard to stay exactly with their calendar when you have kids and a busy life.. I start with the first workout and do them in order but I don’t stress if it doesn’t line up with the week. Like tomorrow I start the third week in Beta which should be a Monday but who cares my body is just happy I’m working out tomorrow. If I try to be too perfect I end up quitting. Just check off the days as you go.