I submitted a on demand discovery scan today at 10 Mar 2018 3:48PM GMT and when I check scan status it is still "Submitted". I set the scan duration for 1 hour, but it does not appear that the scan has even started yet. Can anyone tell me how long it takes a scan to change from "Submitted" to "Running"
I am assuming you mean Discovery to be a WAS Discovery scan; First I would log a ticket with your TAM to get them to take a look; it should not take that long.
They will need to know if the scan is external or internal; if internal it could have something to do with the capacity of the scanner.
I have seen the same behavior you may want to re-launch and cancel the original. If you still see it log a ticket to get them to investigate.
Also is it behind a load balancer/Firewall those teams might be able to add information as well.