This is editable field displays the frame number (position in time) of the selected key. You can enter a new frame number or enter an expression to move the key to a frame.
You can type any expression into the time and value type-in fields of Track View. The variable 'n' is predefined to stand for the key time or value. The expressions can be as complex as you want and can involve any function the expression controller uses. For example you could have an expression like: n/2+sin(n)*40^n.
Key Time Display (Track View): Displays the frame number of the selected key. You can enter a new frame number or enter an expression.