I have had issues with the clock disappearing in my 2017 Elantra Limited w/NAV.

Hello, you can certainly reach out to Hyundai customer service (search their web site for email / phone info), and lodge your concern. However, I don't see it making them work any faster to resolve what is likely a software problem involving one of their suppliers -- the folks who make the audio unit for your vehicle. Sometimes fixes take time. I can understand this is frustrating. I'd probably order and stick on some kind of alternative clock device in your vehicle in the meantime. I know this is important to you, but in the grand scheme of things, I'd tolerate a clock concern instead of an engine stalling concern (or AC concern...)! Good luck!