With my son, I stopped at the end of the pack, and got my BFP 4 weeks and 5 days from the 1st day of my Withdrawel bleed.
I stopped this time TTC mid pack. I'm on cycle 2 now. I had my usual withdrawel bleed, followed by my first "real" period at the end of the next cycle.
My periods are a guessing game when I'm not on the pill though, so CD 29 today.
Also, if you have problems conceiving, the first cycle (from WB to real period) won't be counted in your time TTC, because even though it's possible to get pregnant, your supposed to wait that month out before starting TTC to let the pill get out of your system.