Thanks for comments. Reason I want to do this is to make sure that all my plants switch to flower on same time, which is not the case for all my strains. I had some strains that took much more time to switch and hence had A less favorable weather to finish than those who switched as planned. A good example is 2 different Maple Leaf Indica phenos I had this year who were very late to flower compared to 5 other strains I grew alongside who had same environment and grow conditions (3 months veg, same soil, water etc).
Doing 2 days darkness, if done on august 14th shouldn't hinder my yield nor stretch as stretch happens mainly in september. Note that I'd rather do this on 2 days then having to shorthen days progressively on A much longer timeframe as this would need me to operates in greenhouse every day. I need minimal work for maximum results