The NIP has to be posted so that, in normal circumstances, it will reach the registered keeper within 14 days of the alleged offence. If the registered keeper returns the documentation saying that someone else was driving, then of course it will take longer to reach the driver.
If you wish to challenge the prosecution on the basis of breach of timescales you will have to decline the offer of a fixed penalty and plead not guilty in court.
If a NIP is sent outside the timescale it does not automatically prevent the matter proceeding but the prosecution will have to convince the magistrates that they exercised �due diligence� in trying to get the NIP delivered on time. Bear in mind that if the alleged offence took place before Christmas then, in deciding this issue, magistrates will normally allow extra time to take account of possible postal delays and public holidays.
Bear in mind that if you are nonetheless found guilty it will almost certainly cost you more than �60 and you may be awarded more than 3 penalty points.