I've never waited more than 15 minutes for my registration cards and don't know of anyone who didn't receive theirs "on the spot" like I have. I believe the rules give them 10 days in case there's an issue with the background check.
I know quite a few people. Almost always the process is about 2-3 hours for first time, and about half that for subsequent registrations. But I do know a dozen people who came after tend days and had to return another day.
.If the firearm registration has expired ( previous issued) Take NO action, no need to renew
FYI as if yesterday DC MPD will still not replace cards that already have an expiration date on them with a no expiration date card. meaning for example if you have to show your expired card -- as I have -- at airport or to anyone who may not be familiar with the fact that the expiry is null, you look like you are trying to present an expired registraion