Opening hours 9 AM, Mellow. By the way, I finally got enrolled in IMSS! It took a while, because I needed certified, apostilled birth certificates of both me and my wife- officially translated into Spanish- to satisfy them, here in Cancun. This took a while, because my wife was born in Germany. Those in hand, it went smoothly. ___________________
But they close the doors at 1 pm. You can often talk your way in after 1 pm but it is not guaranteed. Lawyer types and their employees come and go without problems. Better to be in line before 9 am if the weather is not too bad, or go late morning, after the 9 am rush and before the 1 pm last minute crowd.
I usually go around 11 or 12 and rarely wait more than 20 minutes. What takes me the most time is figuring out which line I need to be in hahahaha