The IAS will reject an appeal.
The “consideration period” is to allow you to consider whether or not to accept the terms of the contract, and leave if you don’t. If you decide to accept them, it doesn’t apply. It’s to prevent them ticketing people who enter and almost immediately leave, for whatever reason.
The “grace period” allows time to find a space and park and pay once you’ve been spotted by the entrance cameras.
You don’t get to add the two together, they are different things for different purposes.
This is what the operator and the IAS will say, I’m sure, and it’s also my understanding of these two different things, no matter how helpful it might be to combine them to suit your circumstances.