hollands climate compared to US

hey i was looking at femaleseed.nl and i saw that the strains that i bought (purple power and easy sativa) start to flower in mid-july in holland. im j/w, how does hollands climate and growing season compare to the NE US? if it says it will flower in mid-july in holland, can i determine what time it will start to flower around here? when is hollands growing season? or would it still flower the same time around here - i hope not cuz i jus planted in early june and they wouldnt be big at all if they start to flower in july. i want them to start in like august u know, so i can have some more time for veg. growth? any help is appreciated, thanks alot