How long does the museum take ?

As long as you want it to

The museum itself is small. There are short "video" histories that are sort of campy, but the museum can be enjoyed in a short time- a leisurely 2 hours, probably. Outside there are excavation sites that are pretty cool, too. And, LACMA is right there, too.

Depends on you

It depends on what you do really

It's a good 2 hours, longer if you watch the movies

If you stop, look, read & interact, and take photos with everything, it can take a couple hours