Avg. Time/Page Accuracy

Hi,

We are trying to ensure accuracy in our Time Spent/Page Metric. We want to exclude Page Views of a page for single page visits (in other words, only include page views in the denominator that aren't a single page visit. We currently don't have that segment for the numerator (total seconds spent). Do we need to have that segment in the numerator to get this metric correct? In Adobe, we put this calculated metric on a freeform table with a segment of the hit of the page we are interested in above it and then our dimension is usually month.

Any thoughts to help?

Thanks!