No way of accurately being able to answer that as all growing conditions and strains vary...If you want to increase likelihood of a hermi just do everything wrong! Put a fan blowing straight on the plant you want to hermi...randomize the light cycle...starve it one week...overwater it the next...touch it frequently...etc
just fuxing with the light cycle might not make it go hermi on you...if the strain is very stable you need to really do the nasty to it to want to stay alive...i.e. cut the bitch lol