You were told right. As far as how many times one must do it, I would say, as many times as it takes for you to realize that you are not the meditator.
Meditation, atleast the kind you are describing, provides stillness in you. Usually, you are filled with turmoil. This why suffering is experienced, because the insides are in chaos. When meditation is there, stillness comes. So as you start practicing meditation periodically, you start shifting from moments of turmoil to moments of peace, and again moments of turmoil to moments of peace, over and over. By and by you begin to realize that whether you are in the state of turmoil or the state of peace, you are there to perceive both of them come and go in you. So you must be earlier than them. You cannot be the feelings, because when one goes and the other arises, you are there to watch one leave and the other arrive. Up until now you have felt your existence depends on the feeling, but you start to see that the feeling depends on your existence.
And this is when real meditation begins to kick in. You stop identifying with the temporary states and emotions that rise and fall in you, and remain as the detached perceiver of them. Untainted by them. When you see them for the cyclical comings and goings that they are, you stop attaching yourself to them, and you are free.