Is it ready to harvest?

Lass sie jetzt 24 std. dunkel stehen und dann würde ich sie ernten

Its day 71 since i planted the seed

What week of bloom are you in? If this agrees with the breeder's statement, you can dare. From the photos I would wait a little longer. The pistils still look a little too light and the trichomes should be a little amber. It's hard to say without magnification. Whether after 24 hours of darkness you can continue flowering, I'm not sure, but it should be possible in the final stage. Otherwise the plant looks great.

I already turned off the lights.. can i turn them on again after they stayed in the dark for 24h or boe the damage is done?

Not quite. Wait until there are about 98% brown pistils and this should put you in the "10-30% amber trichomes" zone without having to look too hard. Looking pretty good though!