It's an average of 12 hours for every plant on earth (assuming no shadows from mountains, other plants, etc).

The higher the latitude the more uneven it is (up to 24h in summer and 0h in winter for the poles).

Try being a Cannabis plant in a grow box.... forced into a grueling schedule of feeding and photosynthesis under lights so bright they could actually be on the surface of the sun. Forced to vegetate and create more leaf surface to photosynthesize even more while bathing in a constant flow of CO2. Only to have your reproductive organs chopped off and burnt. It's not all fun and games if you're Mary Jane...