Holy cow, I wrote a book!
Ian Boyd wants to know
why the specific value of 500ms was chosen as the edit delay
in Windows Explorer.
Because it's your double-click time.
Since the double-click action (execute)
is not an extension of the single-click action (edit),
Explorer (and more generally, list view)
waits for the double-click timeout before entering edit mode
so it can tell whether that first click was really a single-click on its own
or a single-click on the way to a double-click.
If the timeout were shorter than the double-click time, then
double-clicking an item would end up having the first click trigger
edit mode and the second click selecting text inside the editor.
(If the timeout were longer, then everything would still work,
but you would just have to wait longer.)
"Through my testing it does not appear linked to configurable
My guess is that Ian changed the double-click timeout not by
but by whacking a registry value directly.
The values in the registry are loaded and cached at logon;
you can update them all you want at runtime, nobody will care.