There’s a 30-day term, and I need to account for 2 days off by extending the term to 32 days. Can use the term like this?:
Term: 01/01/19 – 01/02/19 (2 uncounted days on 01/05/19 and 01/13/19)
Your context isn't clear, but I don't think "uncounted" is suitable because it can mean that you have omitted, or neglected to count them.
A better term might be excluded, as this makes clear that you have accounted for them and declared that they are not part of the term.