Their primary evidence is the CEO's notes and these may be supported by photos.
IMO, if the CEO's notes (an official record) say that in respect of the period of parking specified in the PCN you were observed at 13.28 and you cannot prove the contrary using the legal test of balance of probabilities, then this would be found as a fact by an adjudicator.
If you can neither credibly claim that you moved and returned during the period or that you parked and remained stationary after the time of first obs then you would not succeed on these grounds.