Being mid-July, I think once you get them to start flowering you could stop covering them at all? The days are gettin' shorter, night's gettin' longer. Of course, this is speculation and depends on your locale and whether your plants are used to getting tons of sunshine.
This is what I would do, anyway . . . but I'm 46 degrees N.

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Rule #3 . . . learn to water properly . . .

...your plants should start to flower anywhere from the middle of july to the beginning of august. being that noone told you this before, understand that everyone who just posted is a noob and their advice should be taken with a grain of salt. just sit back let nature take it's course and be sure to pull the males in time!