When can I begin first pack of Ortho Tri-cyclen Lo?

Im switching from the ring to the ortho pills and I pick up my presciption tomorrow. I will be on the 3-4th day of my period (ive been spotting all along -due to the ring- so I have no idea when I actually started after taking it out). Do I have to wait until Sunday to start or can I start them tomorrow? Will I be protected "immediately" as they say, if I start while still on my period??? Has anyone else done this? I am looking for answers from someone who knows firsthand by experience or because of medical profession.