Weird light state: 4 amber, 1 red

My 5N2 has four bays flashing yellow with “Data protection in progress” and 99 hours remaining, and one bay flashing red and says “Failed”. Should I pull that one and put in a new drive, or do I have to wait for the 99 hours to finish?

First thing. Can you access you Drobo and do you have a full external backup of your data?

Assuming you can and have the backup, your Drobo is telling you that you have a failed HDD (red) and that your data is no longer duplicated across the remaining array (blinking yellow) but still accessible.
You should replace the failed HDD with a equal or greater capacity drive. Please refer to Drobo’s recommendations on acceptable HDDs and avoid SMR drives.

Yes it’s still accessible. I’ll go ahead and replace it, and just ignore the message that says “DO NOT remove any drives until data protection is completed.”