Ah, yes. I misunderstood what you meant. Apologies. The 2 days only refers to the 28 days for the registered keeper to notify that the driver was not the registered keeper, hence why magistrates will allow 30 days from date of service (the date the NIP was issued, not received). The NIP itself is deemed good service as long as the date of issue (not actual receipt) is within 14 days of the offence. All in keeping with my understanding of the law. Panic over
The NIP is deemed to have been served 2 days after postage, if your lucky enough receive it on the 2nd day, you have a further 28 days (30 in total) in which you must have returned sec 172 with the drivers details on.
The NIP must be served (received) by the registered keeper within 14 days of the offence, often known as the 14 day rule for speeding offences (see Gov link). This timeframe does not count if the registered keeper hasn’t promptly updated change of address to the DVLA and it went to their old address for example.