Don't think about the abstract concept of "changes" - base it on what will catch the eye of someone looking for this exact feature.
So think about what, in the context of your application, is most distinctive, unique or visual about this feature from the user's point of view.
It'll depend on the application, but if, for example, the "changes" panel is only place in your application where you see strikethrough text next to new text, you could use:
Or maybe its key characteristic is some particular type of list? Then use a variant of a list icon. etc etc
And test it, even if the best test you can do is finding a few people slightly but not very familiar with the application and asking them "what do you think these buttons do" or "where would you look to see changes?".
Then some variant on that mixed with icons you use to represent time, user profiles, etc (depending on which is most relevant to when you expect the "since you been gone" icon to actually be used)