You are probably a bit late to start from seed, tomatoes really need the warmth we get right about now to grow enough to produce throughout the winter. If you started right now you'd be looking at mid-late October for plant out and that's usually when we start cooling down. Not telling you not to try it, but you might also want to hedge your bets with some store-bought transplants just in case.

I usually put mine in about mid-July or early August, which means starting in early/mid June from seed. You can also let your early spring planted tomatoes continue to grow throughout the winter if they're healthy at the end of our hot season...I have a few that made it through the oven and bugs this summer that I'm going to leave in.

Depending on what part of San Diego you're in, you might be able to grow them throughout fall, winter, and into spring (or through summer if you have some healthy ones when it comes that time). I'm in the north county coastal mountains and I grow tomatoes year round.