Well from what I've read over the years it's during the dark hours of flowering when THC production is at its highest.

Also its the extended hours of darkness that increases the flowering hormone to signal it to begin flowering. Keeping the same light schedule through most of flowering is important so it won't be stressed, but nearing the last few weeks you can slightly adjust it for more or less light to speed up or slow down flowering time.

Here's some extra info about flowering, I don't have any copies of growing manuals anymore but found some stuff at http://www.a1b2c3.com/drugs/mjgrow4a.htm :
When flowering the plant indoors, 12 hours light and 12 hours dark is the standard lighting cycle during the flowering phase. However, 13 hours light and 11 hours dark will increase flower size (larger yield) while still allowing the plant to flower. But this will lengthen the time needed to harvest the crop.

An extended period of darkness can also be substituted for the standard 12-12 cycle. 11 hours light and 13 hours dark will reduce the time needed for the crop to mature and harvest, but it will also reduce the size of the crop.

and here another bit from http://www.skunked.co.uk/articles/gr...rijuana-05.htm :
Flowering is induced when the level of a particular hormone reaches a critical point. This hormone is produced during the dark period (night) and destroyed by light during the day. It is important, therefore, to ensure that the dark period is totally uninterrupted by any light , even a few minutes could disturb this sensitive process.

So in a way, yeah it does use the stored energy from the light periods so that during the dark hours the flowering hormone is at its peak each night, which is a result of the dark periods. I swear I'm not crazy, doesn't this all sound right?
GreenDestiny Reviewed by GreenDestiny on . 24 Hour Light Cycle After Flowering Begins? I was wondering if this might get larger buds. normal vegetative light cycle (24 hours) introduce flowering light cycle until flowering BEGINS revert to 24 hour lighting Based on what I know about other plants, once flowering has begun and florigen is coming out of induced leaves no matter what happens to the light cycle, flowering will continue. I also am assuming that a longer light cycle (like that in vegetative) fixes more photosynthates that are being pumped into the buds. Any Rating: 5