How many times in a day should I be doing sandhyavandanam in order to attain liberation? I currently only do it once...Furthermore, what if one is unable to do it more than once due to other responsibilities like education: how to solve this issue?
Mundaka Upanishad III.ii.3:
This Atman is not to be attained by the study of the Vedas, nor by the highest intellect, nor by much learning. Whom the Atman seeks, he gets the Atman; unto him He discloses His glory.
Katha Upansihad II.iii.15:
When all the knots of the heart are destroyed, even while a man is alive, then a mortal beomes immortal. This much alone is the instruction (of all the Upanishads).
Mundaka Upanishad II.ii.8:
Sundered are the knots of the heart, torn off are all his doubts, and the seeds of his karma wear off, when the sight of the Transcendent One is gained.
The Lord is not a bookkeeper. He is not a machine that you put so many coins in to get something. When your heart becomes pure, then the Lord comes running to you.
There is an old Zen Buddhism saying that goes something like this- If you lead a busy life, you should practice 15 minutes a day. On days when you are too busy to practice 15 minutes, you should practice 30 minutes.