recentf-auto-cleanup

recentf-auto-cleanup is a variable defined in `recentf.el'.
Its value is

mode

Documentation:
Define when to automatically cleanup the recent list.
The following values can be set:

- `mode'
Cleanup when turning the mode on (default).
- `never'
Never cleanup the list automatically.
- A number
Cleanup each time Emacs has been idle that number of seconds.
- A time string
Cleanup at specified time string, for example at "11:00pm".

Setting this variable directly does not take effect;
use M-x customize.

See also the command `recentf-cleanup', that can be used to manually
cleanup the list.

You can customize this variable.