Am i wasting my time?

I have this little girl who is around 1.5 to 2 weeks into flower. She is lagging well behind my other two girls in flowering, which have been flowering for atleast 3 1/2 now, all of which where originally from the same batch of bagseed.

currently there outside it is around 12.5/11.5 light/dark
as of the past few days i have been bringing this lagging girl inside and putting her is a lightproof cupboard so she gets her 'ideal' 12 hours dark.

but i am wondering if this is actually doing her any good, will it help her grow more by giving her full 12/12?,
or seeing that she is already flowering (growing about 1.5cm a day vertically) am i causing more harm that good interupting natures course by messing with the photoperiod during these first few weeks of flower?

thanks guys

peace

I dont think the extra half hour will make a difference i think bringing her in and out will cause her more stress keeping her growth shorter.......just my opinion, unless she is a different strand who requires more than 11 and a half hours of dark i dont know of any though. growers use 12 for convience nothing more i dont care what you hear that is the reason, just simple so you can grow multiple strains and flower at the same time. this is just my opinion i am no scientist just from my experience.