My understanding is you do not need to follow any AC requirements - of course some airport staff may not know this, or not care, so be prepared to get aggressive and firm and tell them you're not flying Air Canada so you will be going through and then just go. Don't ask questions, just go.

Having said that, Saturday morning should be less stressful than weekdays, but mornings are always a toss-up and I've seen the United counter very busy. If you can use the kiosk to get your boarding pass, all the better but if you need to see an agent, and have no UA status, budget another 30-40 minutes just for that, and 30-40 minutes for security and 60-90 minutes for US Immigration.