Letrozole help!

ok ladies I went to the doctors today and have been prescribed Letrozole to take on the 4th day of my cycle.. I'm currently on day 2. however he wanted me to get bloodwork done after my period and wait until the next cycle to start taking the pills. Does anyone know how much it would effect my results if I get my blood taken tomorrow so I can start my pills Saturday. I just don't want to wait another month :( I tried to call back and ask but he had already left...