Light cycle thoughts

In late March, I started some plants indoors for outdoor growing. I used the regular 18/6 light schedule. They were put outside early May. Lo and behold, some started flowering. Looking back at daylight hrs for May, I find daylight was less than 14 hrs the first few weeks of May only getting to 14 in the 3rd week or so. Additionally, it was overcast to boot and night temps dipped into to 40s. To be honest, it didn't occur to me about day length. My questions concern minimum day lengths to look for before moving outside, would starting indoors under a shorter light schedule help with the issue? Say 14,15,16 on? It seems that going from 18 on to <14 plus cool temps is a recipe for triggering. Thanks.