Not sure about the zoo...never been. We spend most of the day at Sea World. The shows are spaced out so you can watch them all but will take a while. I love the shows!
San Diego Zoo can easily be a full day activity if you really stand and look at the animals closely/for awhile. I think I spent like 11am-3:30pm there last year and that was with a okay amount of time spent looking at animals (though we did walk quickly past some, and we didn't get to every single area), eating, and taking the little bus tour they have. I would definitely budget an entire day and I wish we had stayed longer but it was really hot and Disneyland had tired us out the day before!
Depends on which zoo you mean. The one in balboa park can easily be done in half a day spending on animal watching. The safari park zoo plan a full day. Sea world can be done in a day also. The shows are spread out to where you follow your group from one to the next just look at times and plan ahead.
Ya we were at SeaWorld for a full day and we didn't have enough time to check out everything we wanted. I think a lot of that was just wanting to make sure we got good seats for shows though so we'd show up 30-40 minutes before it started. We arrived around 11:30 though due to traffic....were hoping to be there for 10-10:30 when it opened
I'm a local to San Diego and consider both of those full days. We have memberships to both, so we can pop in and out whenever but you definitely won't see everything if you're not there all day. Both have a lot of stuff to see/do.
We did both just recently. It probably depends on if you are traveling with kids. We had a five year old with us. We were at sea world from 9am until 4 on Memorial day Monday. We could have stayed until dark as adults only. The zoo we were there at 9am and left at about 1:30. Didn't see everything, but it was alot of walking and felt like we had seen plenty. We also had plans to drive to Anaheim that afternoon and wanted to leave by 2:00pm.