Hi everyone, thanks for your input!
There's currently a bug open for this. It is still being discussed internally on how to best address it. If you would like to be updated on the status of the bug, create a ticket with Customer Care stating that you're missing Average Time Spent on Page, and mention bug AN-130920. The agent can tie your incident to the bug from there with minimal hassle.
It was mentioned that 'Average Time Spent per Visit' will give you similar data; the only difference is that if a page is viewed multiple times in a single visit, they are combined instead of separated. For example, If you spend exactly 1 minute on the following pages:
A > B > A > C > A
Average Time Spent per Visit should show 3 minutes for A, 1 minute for B, and 1 minute for C. Average Time Spent on Page would show 1 minute for A, B, and C. However, in the following example:
A > B > C > D > E
Average Time Spent per Visit and Average Time Spent on Page would be exactly identical. Hope this helps!