Birth Control and IVF

When did you start BC during your IVF cycle?

I am entering my first IVF cycle and my NP called Thursday to let me know she called in birth control for me and that the IVF coordinator assigned to me would call Friday (yesterday) with instructions. She never called. A google search showed most start BC on first day of their cycle and all signs point to me starting my period today. Should I start my BC today even though I was instructed to? The office is closed until Monday.