Figuring they would have the best public bathrooms in the area, I wandered in on a Wednesday around 4:30. After I used the bathroom, I realized the bathrooms aren't public (nor very nice) and I was already in the museum! Apparently they open it to the public for free from 3:30 - 5:30 on Wednesdays. It was a lovely treat, especially since I've been meaning to check out the museum for awhile! I'm going to have to start wandering in on more Wednesdays since an hour wasn't nearly enough time to see everything.
I highly recommend the dinosuars and walking through the bat cave - if you can bear it!
Downside - lots of families, kids, tour groups, etc. Upside it wasn't insanely busy like some museums can get when they're free (yay Canadian apathy?)