Yeah exactly right. I had to get them to introduce wording into my KPIs saying something like “Taking into consideration any extra project work I am asked to complete”. This means I can freely do both but my annual/quarterly review is judged fairly taking it all into consideration.

Not sure what the contracts are like where you are but here in my country that clause about extra duties and overtime when necessary can be defeated by doing a little of what they ask. 30 minutes of overtimes satisfies that contractual obligation as they never state X amount needs to be done. Same for extra duties. Do it once and at the min and thats your obligations fulfilled.