Going down from a 18hr light setting to anything less will in all probability trigger the plant to flower. The problem that occurs is that from the Spring Equinox to the Summer Solstice sunshine increases. Your plant, when it becomes acclimated to being outside at this time will be able to detect this increase over time and can return to a veg state. Even after the natural photo period starts to decrease it takes a plant a month or so to realise it is time to start to set abundant flowers for the reproductive cycle of its life. It's a tricky question, inside you are God and can control all aspects of the plants life. Outside you can not change the seasons. This does not say you can not over come the situation, but it requires a rigid system to be set in place and involves you to be on hand at very specific times. Grow your plants under lights and place them outside. After a very specific time period(say 11-12hrs), return all your plants to TOTAL darkness. Once the natural photo period decreases past your set time, you can leave them out all the time. You are only limited in number of plants to the available space required for your artificial night period. In a way you are playing god again and controlling your plants cycle. It involves a bit of work and time on your behalf to succeed. The system works, having seen it in operation successfully. Don't know if this answers your question, but there you go.