The advice here is all good.
The point above is one it took me a while to internalize: that Stamps, and QuickStamps, despite their apparent similarity, are quite different things.
Operational lesson: it’s almost always worth creating a “real” Stamp. That’s because: a Stamp can include a sequence of actions; it can evaluate expressions; and (probably most important) it can be stored so it’s always available for, yes, “quick” use. QuickStamps aren’t saved in the same way.
For instance, in this case, you could create a Stamp with the action
$MyDate=$Created. Then you assign that stamp a keystroke shortcut, via the Apple menu, or something like Keyboard Maestro. Then, whenever you want to make this date transformation, you just select the note in question and hit the shortcut key – Cmd-8 or whatever you’ve set up.
Also be aware of something implied in the preceding discussions. Two similar (in fact identical) terms, Action when you are creating or editing a Stamp, and Action in the Inspector for a note, mean different things.
The Action that you create with the Stamp Inspector, as shown with the red highlights below, is the sequence of commands that will take effect on notes you have selected and to which you apply that stamp.
That’s the “action” portion of a Stamp. The Action that you create for any specific note, will apply only to newly created child notes of that specific note. If it does not have any children, the Action has no effect. Any children already there before the Action is created will not be affected by it.
So: Stamps, and QuickStamps can both be quick, but they work in different ways.
And the Action in the stamp inspector, and the Action in the normal-note inspector, have underlying similarities but also important differences.