Try and match your indoor "lights on" cycle to sunrise and sunset times and do not put your plants outside until there is at least 12.5 hours between sunrise and sunset, this will ensure they don't freak out and start flowering straight away once you put them outside. Even though 12.5 hours may seem like a slim margin, there is enough ambient light pre sunrise and post sunset that will provide enough light to "tell" your plants that the days are getting longer, so no flowering yet.
Since we are already past the equinox, this should not be a problem. so as soon as your indoor plants are big enough, they can go straight outdoors. If you have the right spot to grow them, why not just start them off outdoors from the beginning? This way they will not need "hardening off" or "acclimatizing" to sunlight. If you start them indoors, they will need a week - 10 days in "dappled" light to get used to the extra goodness in sunlight over the limited spectrums found in electric lights. If you did start them outdoors, you can skip the 7-10 days in "dappled" light, meaning your plants will power through without any hiccups or stagnation while adjusting to sunlight. As long as temps are 15+ degrees Celsius, they will grow ok, just not fast, but will really take off as it warms up. If you have a south facing wall that receives a lot of direct sun during the day, having your pots next to this wall will provide some extra radiated warmth at night, keeping your plants happy and cosy.
If starting indoors after all, give the around 13.5 hours of light, set roughly to sunrise and sunset times + a half hour earlier and later than the actual sunrise and sunset times. This way the transition between inside and outside will be smoother than going from say 18/6 indoors to 13/11 outside, which will freak them out. Another factor in this situation and the seemingly shortish lights on time, is that your plants need to be a certain age before flowering can begin, so the first 5 weeks with shortish day length will not cause your photoperiod plants to start flowering.
As long as the days are getting longer (increase of time between sunrise and sunset), your plants will also be prevented from flowering.
Hope this helps,..........
Organoman.