after all danger of a frost is over plant them. i live more north i plant around june 1st but thats the normal date to put plants out here. you can check when people plant their tomatoes in your area this will be the same time you are safe to leave yours out.
no they are annuals when grown outdoors. the only way to keep one going is to put it under 18-24 hours light and keep it as a mother for next year i assume you want to grow the same plant outdoors again. if you have one outdoors youd like to keep for next year cut some clones of it keep one of the best looking under said lighting. trim if nesessary and cut clones in early spring for outdoors.
The earlier u put it out the bigger it will get. But u could get a freak snow storm an kill it early. Remember last year on march 23 we got 2 ft of snow out here on the prarie.
I have a batch of seedlings started now in feb that will go into the ground in late march-april, I use the cutdown-2liter green houses for a week or 2 .
I get another batch ready that will be ready to plant in april -may.
Remember to harden them outside before u transplant em for a week .
that chart will tell you when the light cycles change so you can veg em outside. just put in your latitude and the date and as long as theres at least 14 hours of light a day you can veg. any less than that and they'll flower and stunt growth a lot going back to veg.