..."can't put the clock back" doesn't literally mean that you can't change the time on a clock. It's referring to not being able to go back and change things that already happened.

This is true. There are things that, once done, cannot be undone. You can try to fix their consequences. You can change what you do going forward, so that the thing would not be done that way again. But you can't, say, un-kill an executed innocent.