Rightly or wrongly I count it from the extension expiry date, in my case 29 April, so therefore 29 May (30 days), 29 June (31 Days), 29 July (30 days) so total of 91 days, in case months are being counted as 31 days each it's safe to move on August 1, by doing so I had no issue with my local office 3 days ago for my annual extension.
I personally think it should be from the approval date not from the expiry date, but is it worth the potential problem next year for a few days this year.