How much time should one plan to spend here?

I plan on 1-3 hours with my daughters. They are 8 and 9.

I only ended up visiting the air and space museum, but I'm a huge plane and space nut and spent three and a half hours and loved every minute! Thank you all for your help!

There is a ton of history about all kinds of flight. A true enthusiast could spend a whole day easily. With Children 1 to 2 hours.

Probably an hour for casual viewing, all the way up to about 3 hours for big air/space enthusiasts.

Maybe an hour. If you have kids that really like to look at things and play then maybe a little longer.

I would plan a day trip and buy day passes for all the museums... we always do a 2 day and spend the other day at the SanDiego zoo cause its right next to the museums... otherwise depending how interesting the museums are u could spend a couple hours in each one if u have a slower pace