SeaWorld is easily done in a day. If you come during SeaWorld Summer nights, then there's more activities (shows) after dusk. I actually like the Summer Nights shows better than the day shows.
Legoland is in Carlsbad and about 30 - 45 minutes North from SeaWorld.
Knotts is only a few minutes from DL.
Universal is North from DL and it's about 45 minutes with NO traffic. Depending on when you go, it can take up to double (if not more).