Shane from MIGRO recommends using UVB in the last 2-3 weeks of flower for 2hrs(@24″ hanging height for his migro310 lamp) mid light cycle. This simulates mid day when the UV is at it’s peak in nature. So if your 12/12 cycle is 9am-9pm you turn on UVB at 2pm and turn off at 4pm.
I run Shane’s MIGRO310 along with a California Lightworks UVB in a 5×5 much closer than 24″ so I only run my UVB for an hour.
Hope that helps! 🙏
