Disk Utility First Aid has no progress bar? It is on "Checking snapshot 1 of 4" and has been for 30 minutes. 

There is no progress bar. The drive is a 1TB SATA drive. 

Should I quit it and start it again or just let it chug?
It was indeed stuck. We ended up force quitting the process. 

It appears from other testing that the drive is operating at a much reduce top speed. Hopefully it is not failing. But this process was definitely stuck.