When you say day length are you including dawn and dusk? Cuz the plant senses changes in light so it uses the dawn/dusk included when figuring length. Either way, there will be strains you can find that will work, when grown outdoors it is more heavily reliant on whether the length of day is increasing or decreasing to trigger blooming, and not strictly over or under 12/12, since a perfect and instant switch from 18/6 (or 24/0 for that matter) to 12/12 is only possible indoors. Outdoors, generally, plants will veg as long as the days are getting longer and bloom after the solstice when they start getting shorter. Think about this, there is a TON of weed grown outdoors in mexico, which is also very close to 19 degrees latitude, so it definitely works. That being said, a strain that was bred in a much different climate will have more trouble adapting, so try to find something local.