Okay so correct me if I am misunderstanding but this is the predicament.
The police have 6 months from the date of the offence to start proceedings, otherwise it will time out. However, to combat that, most police forces will start from 4 months and if the ducks aren't in line, just go straight to SJP in the interest of not letting it time out.
So we can either respond the S172 asap to try and ensure we get in there before the police go straight to SJP. Or we can slowball it, complete it on day 28 from the NIP we have received and hope they aren't on top of everything and ultimately it times out.
I guess it would come down to whether or not you feel lucky... Well do you punk?