ROG:
I found an initial 20 day limit after completing mod 4
gov.uk/become-lorry-bus-dri … -qualifiedWaiting for your card
You can drive professionally if you’ve passed all the tests and you’re waiting for your Driver CPC card to arrive.If your card doesn’t arrive
You should get your Driver CPC card within 20 days of passing the final test. Contact the Driver and Vehicle Standards Agency (DVSA) if you don’t receive it.
That makes sense, though even then I doubt you’d be limited to 20 days driving if you phone the DVSA and tell them it hasn’t been delivered.