org-fast-tag-selection-single-key

org-fast-tag-selection-single-key is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means fast tag selection exits after first change.
When nil, you have to press RET to exit it.
During fast tag selection, you can toggle this flag with `C-c'.
This variable can also have the value `expert'. In this case, the window
displaying the tags menu is not even shown, until you press C-c again.

You can customize this variable.