if your plants are in bloom and you had one light get stuck on for a whole month it will probably just keep your plants from blooming at all and if the were already blooming and this happened it will put them back in veg .... and the buds will begin to stretch...
three options
1. put them back in veg for another 6 -8 weeks then put them back into bloom
2. fix timer and keep them in bloom and hope for the best.. maybe no damage but if they get leggie and stretch into thc covered rope make bubble hash out of it.
3. chop em now and dont waste your time and electricity
good luck