In terms of timescales, the original PCN was served by a CEO to the car. There is then a period of 28 days for the PCN to be either paid or representations submitted. After expiry of this time period, the council can serve a Notice to Owner on the registered keeper of the car, which is the hire company. The hire company then have 28 days in which to submit reps on the basis of their being a hire company, naming your company as the hiring party on the date of the alleged contravention. The council, on receiving those reps, can then accept them and cancel the NtO and serve one on your company. They have 28 days from cancelling the first NtO to serve a second NtO.
The PCN was dated 24th November, so you can work out the approximate end date of the period within which they must serve an NtO on your company. At the moment, I don't think they are yet out-of-time.
You say you are expecting a PCN but it will be a Notice to Owner. May I assume the original PCN was never seen on the car ?
As for the possibility of grounds for a representation, the council photos show the car parked right next to the sign stating the bay is for permit holders only Mon-Sun 8.00am to 11.00pm. PCN is timed at 18.05, so well within the restricted period. A PCN is shown as on the car.