Including within the fee is an allowance of 3 days for a QS. Assuming the QS works 5 days a week within the Working Area (Site), when assessing a CE under option C can I offset the QS cost already allowed for within the fee and assess the recoverable cost under Defined Cost as 2 days?
What is in your fee is actually irrelevant.
To assess whether you get anything extra for a CE, you have to demonstrate the change in Defined Costs due to the CE. So if the QS is based in the Working Areas for 5 days a week and has to work a bit late due to a CE, but doesn’t get any over time, then there would be no effect.