Switch from IUD to YAZ?

I had my IUD out Monday Nov 15 after months of problems and was put on YAZ. I got a short 2 day cycle (the following thurs & Friday) and then did a Sunday start. I want to know how long it TRUELY takes to be effective. The pamphlet said 7 days and I've heard others say 30 days. So which is the truth? And was that 2 day cycle really a cycle or should I not have even counted that? Only serious replies please! thanks!