I agree. Indoors is best, since it is late July and will be very hot and humid. Also early is best too for the same reason---it should start before noon, since the afternoon will be really uncomfortably hot.
Hey, I write for the Houston Press Art blog was hoping to do a little write up on the Houston Sketchcrawl. Would any one be willing to answer a few short questions? Maybe the blog can help get some more sketchers involved. Hit me up with an email - email@example.com