I tend to use them from about cd8 because I don't really know what's happening with my cycle after coming off BCP. I've also started using the CBFM this cycle which has just added to the obsession - as soon as I got my first high reading, I started on the OPKs again!
If you're going to start this early in your cycle though, i'd recommend getting some internet cheapies so you don't go bankrupt!! Good luck
