The best way to tell when to harvest is comparing your preference to how your trichomes look. Just give it a quick google and you will find info on it.
Green Poison Fast Version Flowering Time:
The specified indoor flowering time for Green Poison F1 Fast Version is typically 6 to 7 weeks (or 42 days), making your current timing very close to the standard harvest point.
What to Check Now:
While the calendar is a good guide, the most accurate way to determine if your plant is ready for harvest is by inspecting the trichomes (the tiny, mushroom-shaped resin glands on the buds and sugar leaves) using a jeweler's loupe or a magnifying glass with at least 30x magnification.
My recommendation is to get one of these: https://url-shortener.me/2QLM
Then you can also post more detailed pictures, for better analysis.
Most growers aim for a mix that provides a good balance of potency and effect:
Optimal Window: When 70-80% of the trichomes are Milky/Cloudy and 20-30% are Amber.
For a more energetic high: Harvest when the majority are milky/cloudy, and only a few are amber.
For a more relaxing/sedative high: Wait until 30-50% are amber.
Hope that helped! π