We went to the exhibit last Monday. The first time slot is 10:15 and then every half hour after that (10:45, 11:15, and so on) We got in line at 9:25 and there were only a few people in front of us. At 9:30 we could have took 10:15 tickets but went to the front of the line and asked for afternoon tickets. We got 1:15 tickets. This worked well for us since we had 10:00 tickets for NMAAHC.
We arrived around 1:00 so spent a few minutes in the gift shop. At 1:10 they placed a 1:15 time on the board so we got in line. The staff were very helpful and friendly.
There are 3 rooms and they don't take very long to get through. In fact you only get 30 seconds in one mirror room and 1 minute in the other. We didn't mind leaving our bags outside the room. There aren't people milling around. Just a staff member and people lined up (not near the shelf). We enjoyed the exhibit and took loads of pics.
Afterwards we went upstairs to see the other exhibits. We left around 2:30.