UVB is 280nm - 315nm.
UVR8 universal resistance locus 8.
95% of stress response from uvr8 protein happens at a peak of 285nm.
The response at 285 is 10x that of 290nm. The curve is extreme.
Anyone that says UV doesn't increase thc are both right and wrong, well technically it doesn't directly increase but it does dramatically increases the concentration of trichomes in order to better "sunscreen" itself from exposure.
It's important to find out the peak NM emitting from the bulbs otherwise no point in using peak 310nm.
UV doesn't use a photoreceptors like other colors of light. It uses a salt bridge dimer for detection, and requires very little exposure to burn the salt bridges and activate uvr8.
3x24w I'd go with 2 hours to start, really should be done from start of flower.
Fluorescent bulbs are coated inside with ...... Some shit I forget, each time you turn it on it burns out a little. Some treatments advise multiple on offs per daylight but this will destroy your bulbs ultra fast.
The way UV is measured is in dosage over time, I imagine you could possibly overdose given your mid flower
Be sure to supplement blue light or add a little veg spectrum, blue light is used to drove a DNA repair mechanism called photoreactivation.
Applying UV with no blue is a death sentence.
The 285nm photon breaks the salt bridge dimer, damaging DNA helix. Using blue light the plant converts blue and violet light to create enzymes called photolyase. These accelerate DNA repair allowing the plant to repair 100% of helix damage.
DNA itself may be a photoreceptor, the UV needs to "burn" in order to gain access.
UV light is responsible for control of hy5 (elongated hypocotyl 5) this is more or less the central hub network for everything else,
The firmware.
Welcome to the wonder of Ultraviolet.