not all plants need dark , cannabis is in the group/type that do actually grow better under 24 hrs light , obviously thats "growing" and not flowering , a photo strain will need the darkness to flower
for growth , its been biologically proven cannabis grows something like 30% better under 24 hr lighting
not trying to step on anyones toes or argue , just posting up some professionally proven fact , not all plants are the same when it comes to light/dark/co2 etc
peace
p.s. its my belief autos will grow bigger under 24 hr lighting but also take a bit longer , but only if everything else is optimal , if the root zone gets stunted it wont recover nearly as well without rest , but thats all just my belief