@cgsrimi your google street view link doesn't work, please see the guidance at the bottom of this post (https://www.ftla.uk/civil-penalty-charge-notices-(councils-tfl-and-so-on)/read-this-first-before-posting-your-case!-this-section-is-for-council-tfl-dartme/) on how to share google street view links.
The wording at this stage can be very simple and to the point:
Dear London Borough of Hackney,
The alleged contravention did not occur because at the time of parking, no suspension signs were present. I parked my vehicle at 2 pm and I have since been informed by your colleagues in the suspensions team that the signs were only erected at 2:30 pm, so there was no adequate notice of the suspension. Considering these are residents' permit bays, it is hard to conceive of circumstances where a notice period of less than 24 hours could be adequate.
I look forward to your prompt cancellation of this wrongly issued penalty charge notice.
Send this online and get a screenshot of the confirmation page, in the meantime I'll get the proper suspension logs.