You seem to have the wrong idea about this.
You cannot challenge a NIP. It is simply a notice informing you that a prosecution is being considered.
What is of greater importance to you is the accompanying “request for driver’s details”. Unless the police formally tell you that action against you has been discontinued, you must respond to this. If you fail to do so you commit an offence which, on conviction, carries a hefty fine and six points. Any details of the speeding allegation, including the possible error with the location, then become irrelevant.
The police might respond to you before you are due to reply to the request or they might not. As above, they only aim to respond within ten days. They have no obligation to do so – in fact they have no obligation to respond at all.
In my view, what you need to do is to respond to the request by saying that your vehicle was not at the location mentioned at the time specified so you cannot provide them with the details they require. Do his either on the form provided (if there is an appropriate section) or by means of an attached letter.
There is no point in delaying this. If the police do respond to your query in time they will either say the matter has been discontinued or they will still require a formal response to their request. If they don’t reply in time you will have to respond anyway.