What determines when the Add Bookmarks Dialogue auto-closes?

Hello, I am a keyboard user who presses ctrl+D to bookmark webpages. I then wait for the Add Bookmarks Dialogue to disappear and sometimes after a few seconds it does, whereas at other times it doesn't and so I will have to manually close the box. I am wondering what circumstances determine whether the box auto-closes or not? I have tried googling and found old posts talking about some auto-close timer being started if you move the mouse pointer or cursor, but that can't be the answer here. Each time I am literally just pressing ctrl+D then stopping to see if the Add Bookmarks Dialogue will close on its own or not. P.S. I am also not confusing adding a new bookmark withh editing a previously added bookmark. I know that the Edit Bookmark box doesn't auto-close.