I got a DUNS number a couple months ago, and I got the number the same day.
According to their website, it can take up to 5 days, and expedite requests won't actually speed this up
After requesting a D-U-N-S Number, please allow up to 5 business days to receive your number from D&B. Expediting your D-U-N-S Number creation process will not shorten this waiting period. If your application has taken longer than two weeks to process, please email D&B.
Once you receive your D-U-N-S Number, please allow up to 2 business days for Apple to receive your information from D&B. After this period, you may enroll as a company/organization in the Apple Developer Program.
To update your D&B profile, please email D&B. It takes up to 2 business days for D&B to provide updated information to Apple.
1 thing to be careful of: After you get your DUNS number, you'll get a link to register in iUpdate. If you don't do it in time, they'll block your account, and you'll have to mail a notarized letter to unblock it. (not kidding)
With Mexican companies it takes around 3 weeks 😞 although from what I read, USA based companies take less time.