If you get them in the ground by June or july you should be good. I'm not hugely familiar with outdoor growing, but from looking at your grow and pics one of my friend sent me on snapchat, it's a bit early in the season which is why they are wanting to flower already. As the days get longer, the plants will likely re-veg and the flowers basically just fall off. I don't imagine any outdoor cannabis plants will be flowering mid summer. Or you can force re-veg by putting it under 16-24hrs of light.
Cannabis usually takes around 2-3 months to finish flowering, depending on strain, and will veg for as long as it has 16+ hrs of sun. When growing outdoors, you rely on the natural photoperiod to determine what stage your plant will be in. less than 16 will likely lead to flowering, and ideally you want 12 hrs of light for flower. You can make a PVC hoop house or rig up a tent system for the plants and pull a tarp after 12hrs of daylight to make sure they don't revert to veg/force flower. It's a nice way to get a crop for the summer.
If you are having some plants start to flower and some not, I'm guessing it's because it's somewhere in between 12-16hrs of daylight, which is usually the sign for the plants to start to change cycles. In California, they say about the latest you can harvest is Halloween, although if you live in wetter areas it might be sooner than that for outdoor with no weather protection.