Outdoor lighting

When planting outdoors, is there a very specific time (1 month 2, 3, 4?) when the plants move from Veg to Flower cycle?

Or, since light outdoors is not controlled artificially, or manipulated in any way (in lower 48 states) are the plants Constantly in Flower cycle?

Outdoor for photoperiod plants is based on amount of light per day. Typically photos will switch flower when they get below 13-13.5 hours of daylight, fairly simple, check this site for your area and it'll tell you approx. when they'd begin flowering.
http://www.timeanddate.com/sun/

You can also force flowering with a technique called light depravation (or commonly called light dep). Basically you manually or automatically cover them after 12 hours of light every day and force them into flowering.

The other exception is autos, you can flower them pretty well anytime as they automatically trigger the flowering cycle. The more light available the better for autos, they can flower under 24 hours of light.

All depends when you plant them...the long summer days the plants will be in veg and for me usually around august my girls will start to show sex......it all depends what you want ....if you put your plants out in late may they'll be huge ....beginning of July not as big .....because things are done in October ....hope this helps. Not autos obviously

Agree with both responses, and would add that it is strain dependent too sometimes. I've got four strains outside in California and the Blue Widow started flowering this week already. I'm at 14:05 daylight now and typically don't see flowers until second week of August with most strains. Others are all clearly showing sex now, of course.

Agree with all of the above and also think that the temp difference may also play a part.