The payment period gives you an extra 2 days to pay so it's hit or miss with an adjudicator technically it's wrong but in your favour
I'm not sure it's hit and miss at all, I'm not aware of a case where this point has gone the wrong way (at least not where it's been argued proeprly), relevant decisions are:
Adjudicator Decision
Jack Walsh Papjinder Gahir v London Borough of Havering (2180111742, 19 April 2018) (https://drive.google.com/uc?id=1a7yo5Hx8AbMers6U6UX9t44g_KrV0naV)
Teresa Brennan Nima Barani v City of Westminster (2230394347, 07 October 2023) (https://drive.google.com/uc?id=1_GzJ5FCOY71KI-aqVyHOiUARofv1HxG3)
Andrew Harman Mohammed Ibrar Khan v London Borough of Barking and Dagenham (2220496056, 10 August 2022) (https://drive.google.com/uc?id=1UUj1JCtIEy0XlBy3oLQmRAMKh9hdud34)
Carl Teper Syphon Mohammed v London Borough of Barking and Dagenham (2220717880, 05 November 2022) (https://drive.google.com/uc?id=1rUXpmEatR4xoGwwf7cDYM_LLnERz6sCa)
Anju Kaler Mohammad Naeem v London Borough of Barking and Dagenham (2230108572, 13 March 2023) (https://drive.google.com/uc?id=17rqcgPuIll7-yDiwUM5Gs0g1pxS2RIMJ)
Jack Walsh Benjamin Weedon v London Borough of Barking and Dagenham (2230197958, 18 May 2023) (https://drive.google.com/uc?id=1zHSqzQT9wHB9VdI6m_Kc0hZ4T4Gp1u5P)
Cordelia Fantinic Aldina Ronisia De Abre Mendes Delgado v London Borough of Barking and Dagenham (2230347777, 09 October 2023) (https://drive.google.com/uc?id=1ZzWAxRPMCB7vLV66WrPUhuaZT3Fua_-Q)
Carl Teper Stanmore Quality Surfacing Ltd v London Borough of Lambeth (2230281431, 15 July 2023) (https://drive.google.com/uc?id=1pSC7bdoNh1jGfifzq5_jQ1c0ewpLDdse)
Carl Teper Ian O'Flynn v London Borough of Lambeth (2230309483, 26 July 2023) (https://drive.google.com/uc?id=1KU5k-MmvJrj28ERY3tvQ2mbaFmVT0jGT)
John Lane John Duffy v London Borough of Lambeth (2230325752, 12 August 2023) (https://drive.google.com/uc?id=1-pcm3L4Dz489AglMnvyIgzLWYWEzjxtI)
Edward Houghton Zaid Noorgat v London Borough of Lambeth (2230306124, 30 August 2023) (https://drive.google.com/uc?id=1-HL2qHR_4C8bMJ9lK3ph8XuYR9j4jciv)
Henry Michael Greenslade Commercial Plant Services Ltd v London Borough of Lambeth (2230359732, 02 September 2023) (https://drive.google.com/uc?id=1semkrQw38o54RYJELbxvJt3h9nt_rbsB)
Henry Michael Greenslade Stanmore Quality Surfacing Ltd v London Borough of Lambeth (223035970A, 02 September 2023) (https://drive.google.com/uc?id=1cSY4smwW48kGQE7nqfnjrDDFsXvFWclk)
Carl Teper Stanmore Quality Surfacing Ltd v London Borough of Lambeth (2230359721, 04 September 2023) (https://drive.google.com/uc?id=1UWdKm4oRgvlKwrB-FAuMeuvoedA78_F0)
Jack Walsh Stanmore Quality Surfacing Ltd v London Borough of Hillingdon (2230415298, 28 October 2023) (https://drive.google.com/uc?id=17c3SoDqtjkEZewpZLRWgj-8BfO8QuxnW)
The Barking and Dagenham cases are all identical to this Westminster scenario, and as mentioned above we've never lost.
I would make a very simple representation right now:
Dear City of Westminster,
The PCN is invalid because it does not comply with section 4(8)(iv) of the London Local Authorities and Transport for London Act 2003, it follows that the penalty charge must be cancelled.
Yours faithfully,
If the council rejects, I'll be happy to represent you at the tribunal.