Satu deergha kaal nairantarya satkaaraa aasevito dridhbhoomi
Sa: That (abhyasa)
Tu: But (for emphasis)
Deergha Kaal: Long duration
Nairantarya: Continuous, without break
Satkaaraa: With the due respect, with the right bhaav
DridhBhoomi: Firm ground, strong foundation
Having given the definition of abhyasa (practice) as one of the two tools for Yoga, Sage Patanjali goes on to describe how that practice becomes firm and strong.
That (abhyasa) assumes a stable ground after repeated and regular practice for a long period of time, without any breaks, with due respect.
Yoga is not a course or a module to which one can assign a duration, it is lifelong sadhna under the sanidhya of one’s Guru. Niyama, or regularity of practice as prescribed by the Guru, is an important prerequisite for Yoga. It is said every day comes with its own shakti, by missing the practice for even a single day, that specific shakti is left behind, leaving the sadhna incomplete. Also important is to give due respect to the sadhna, giving it priority over other things and dedicating time and effort to it.