It is an interesting experiment in gardening but I am with
@Sueet and the amount of time that the lights are on and the amounts of time till harvest do not sound economical either on a personal or business level. Sort of the usual comparing apples and oranges.
It is more than just the estimated cost of the electricity for the 24 weeks for that growing. Also need to know the electricity costs for a typical 8 to 12 week grow cycle at 12/12 with the same lights.
Cannot compare the estimated $40 a month of electricity for your grow to to the 10K for four lbs of weed from a dispensary. It does not make sense nor add up. Around here very few dispensaries grow their own product. They have to buy from a grower so most likely the four lbs actually cost the dispensary about 5K. They then have to add on all their expenses and hope there is enough room at the end to show a profit to make it worth while.
I believe Sueet brought up your time spent during the grow. Start adding in the money you would want if you were working for someone and having to help grow those plants, mix fertilizers, sweep the floor and all those other chores. Add in cost of the lights and the time it takes to go get them or what the delivery costs. Add in the "wear and tear" depreciation of those lights after they have been running for those 24 weeks. Figure in the costs associated with the room lights that have to be on so you can see what you are doing while mixing up fertilizers, etc. How about insurance? A legal dispensary and legal grower will be calculating the insurance on buildings and employees into the costs of their product.
Also, I was under the impression that the idea behind longer lights on and same or shorter light off times was to reduce the number of weeks till harvest. Instead of the 12 weeks from start of flower to harvest the amounts of extra time that the lights are on allowed a harvest with the same quantity and quality in 10 weeks.
The savings are in time and it is up to the grower whether that time savings is worth the extra costs.