You are right about actual days never being the perfect 12/12 but, photoperiods can vary, yes...but, consistant day to day photoperiods are essential...You cannot have 10.5hours light one day and 12 the next and not end up with problems...this grower just wants to change 1/2 an hour, once! so, the answer is yes you can, and it won't bother your grow at all, regardless of whether you have a timer or not...peace good overall info though.

I do use shorter veg days and flower all the way down to 10.5-11hrs light at the end...emulating a season/fall as close as possible