org-timer-display

org-timer-display is a variable defined in `org-timer.el'.
Its value is

mode-line

Documentation:
When a timer is running, org-mode can display it in the mode
line and/or frame title.
Allowed values are:

both displays in both mode line and frame title
mode-line displays only in mode line (default)
frame-title displays only in frame title
nil current timer is not displayed

You can customize this variable.