OP, for info:
Particulars to be included in a penalty charge notice given under regulation 9
2. The information to be included in a penalty charge notice served under regulation 9 is—
(a)the date on which the notice is served,
(b)the regulatory matters,
Meaning of “regulatory matters”
1. In this Schedule “the regulatory matters”, in relation to an alleged relevant road traffic contravention, means—
(a)....
(b)..
(c)the date on and the time at which the alleged contravention occurred,
Your PCN doesn't state the time at which the alleged contravention occurred, instead it states and observation period. You are left to infer/deduce the time of contravention and the only rational answer is 15.06.
You had parking rights from 15.05.
Yours is one the occasional series of events where parking rights were obtained during the period of observation(and the CEO didn't verify that you were still in contravention before they issued the PCN.