At which time of day to harvest...

I am reading that cannabis produces THC during the dark cycle and that it degrades during the light cycle. The conclusion would be to harvest just after the dark cylce has ended or to even let the plant for 24 hours in the dark.

This seems to be a myth to me, because, once you cut the plant, it isn't dead immediately. So if you cut it and put it in a dark room to dry, the plant still lives and produces THC and whatever, until it is dry.

And also: does THC really degrade so fast that you can not harvest the plant later in the day (light cycle) without losing potency?

Conclusion: it doesn't matter at which time of day/night cycle you harvest.

it is also said that harvesting when the moon is full gives the bud extra potency. the moon cycles indeed have an influence on plants but is that true about harvesting when full moon?

Many realiable sources that I have read (Jorge Cervantes, Mel Frank, Ed Rosenthal) have written that resin production occurs at night on a cannabis plant. I believe this to be true.

I used to harvest just after dark period until I gave both a try with plants of the same mother. I noticed no difference with quality of both. I even marked both to distinguish and gave sample to many friends. One in particular is a gentleman who likes to record all feelings of HIGH. and no one senses differences either.

I feel that one extra night of resin production is not sufficient to feel differences in potency.

The concept of extended dark period before harvest also sounds great on paper because resin is produced at night so give them a loooonnnnggg night and thus more resin. However, this is an unnatural occurrence and can stress the plants just before harvest. The authors I mentioned above all advise to get the most potency out of any strain, it should not be stressed throught its lifetime.

I believe it was forum user Grasso who stated, There is a fine line between the best and the rest.
    

how to choose the best time to harvest indoor...with no moon and artificial light ? martini?

The thing is, the moon is still there, at the same distance from the earth, whether it is full or dark.

There's no difference in the gravity it exerts on the planet when the moon is full versus when it's half, quarter or new. It's just that some of it is in shadow and can't be seen. It's still there.