If you leave out the ticketed special exhibits you could probably hit the whole museum casually in two hours, three if you want to take your time.
About 4 hours could be longer if u do all the shows
2 hours without the ticketed specials is on point. I was there 1-13-19 for about 5 hrs including the Tesla Coil show and the Black Hole Planetarium show which were about 40 mins each.
Thanks! Your answer is awaiting moderation.