I think 5-10 minutes is a reasonable wait time. I would have left, just as you did.

J was in the ER lately. 1.5 hours later, and I approached the nurses station, and said, 'Children's across the street has no waiting right now, I want to have him discharged'. Guess what? A doc was in 5 minutes later. Turns out, they couldn't treat him anyhow...nice bit of triage there, nurses! The doc did apologize, and I was gracious towards him...BUT, 1.5 hours, with a 6 year old? To find out they needed to send him elsewhere?