My co-admin and I are using this tool and have noticed that there are times when we check the box and Change Post Date does not show up on the menu. If we uncheck and try again, it will often show up, sometimes after leaving and returning to the thread. Still testing to see if I can identify a trigger but though I would post in case there are any thoughts on why it might be a bit flaky like this. In general, though, liking it and getting some mileage out of it.
(Use case: I am starting weekly threads and often write them "backstage" in a private forum the previous week, then move them out to a public forum on Sunday when the new one is supposed to "go live". Since I often wrote them days before, I am using Change Post Date to make the post date match the date I make them public. My co-admin is doing much the same.)