yah, i think that outdoor crops finish around late september, early octoboer, depending of course on strain and where you live.. so if a certain strain takes say 8 weeks to finish flowering, you just subtract 8 weeks from say oct 1 to make things easier.. 8 weeks is two months in my book, so two months before oct 1 would be aug 1.. so i would think that around early to mid august you should start to see some signs of flowering going on with your plants..
good luck with the grow..