In reply to Andrew Howell.

Everything is based on individual tastes, whether you read the signage, spend time looking at each/some/very few of the exhibits, hit the gift shop or cafeteria, etc. - I've seen guests at the Florida Aquarium spend half a day there, and I've seen others depart after 30 minutes.
MapQuest says the Sixth Floor Museum is 0.8 miles to the northwest of the Convention Center, so allow time for the walk (round-trip). And when I peeked in (didn't actually go on the last trip), there was a line - not too long but at least 20 people - ahead of me at the ticket counter.