Icons without descriptions have their limits
Each icon likely has a history in context someplace else. While this is more about the design of the interface it does have an impact on the user experience when someone clicks an icon that means something other than expected. Icon design is not easy.
+ (plus) is usually New or Add
✓ (check) usually Valid or correct
x (letter x) is usually
cancel, close, or delete depending on context
Clocks mean timed, time, appointments, history and possibly expired
! usually indicates notice, caution, warning, attention needed
When considering different elements for an icon you want to make sure not fall victim to common mistakes in icon design.
You could use a simple triangle pointing up or down
▲, although triangles typically mean yield or caution, although on Stack Exchange it's vote up. In some applications an up arrow indicates previous version.
You might also use the infinity symbol as icon
∞ for history since a clock is much more complicated than your other iconography. I've not seen it used in interfaces recently so it would be able to be redefined as a visual metaphor.
Since my guess is that you're using it for versioning, you might also use an ellipsis
... to show more.
> greater than symbol to show other, although this is used to represent directories in bread crumb navigation paths, and forward.