I'm new to this, so apologies if I appear ignorant !

I am trying to find out how to calculate a "time out" date ? Have tried searching, but seem to be going round in circles & the PC is playing up, so thought it would be quicker to post a query...
If say, for instance, the "offence" date of an alleged Speeding offence, is 1.3.06, but it was a "Company" vehicle & you don't receive the NIP until 1.7.06, when would it "time out" for S-172 purposes ?
Would it be 6 months + 28 days from 1.3.06 ? OR 6 months + 28 days from 1.7.06 ?
Can anyone please help
Thank you