ktgirl,
It really depends on how much hcg is in your system to how early you will get a BFP
I tested with the internet pregnow ones (who say on the packet that you can get a positive from 10dpo ) but didnt get my first very faint + untill I was actually 12dpo, and it was so faint I mistook it for an evaporation mark. The advantages of waiting untill you are due for AF (or a day earlier) is that you really reduce your chances of getting a false - . Good luck with your TWW, lets hope you do get that