Pradyumna: "Concentration of the mind upon Kṛṣṇa, the Supreme, is made possible by prescribed devotional service in nine different forms, of which śravaṇam is the first and most important."
Prabhupāda: So our yoga system is not like that, that we whole day, twenty-three hours and forty-five minutes, I engage myself in all nonsensical activities, and fifteen minutes I concentrate my mind, the meditation. That kind of yoga system is not here. Here, twenty-four-hours' meditation. Even during sleeping. Twenty-four hours means during sleeping also. Life should be melded, molded in such a way that twenty-four hours you'll be able to think of Kṛṣṇa. So we are engaging our students in so many Kṛṣṇa activities. They are going to the park, chanting Hare Kṛṣṇa, or distributing literature. All these activities, remembering Kṛṣṇa. They have no other, I mean to say, thought except Kṛṣṇa. So this fifteen minutes, twenty-minutes, sitting, is all right. But one who is twenty-four hours thinking of Kṛṣṇa or Viṣṇu, how far he is advanced, that can be imagined. Therefore Kṛṣṇa says personally, yoginām api sarveṣām: (BG 6.47) "Of all the yogis..."
There are different types of yogis. It is, it is not that... Just like we do some other business, twenty-three hours, forty-five minutes, and fifteen minutes we sit down for meditation. No. Twenty-four hours. Kīrtanīyaḥ sadā hariḥ. Sadā means twenty-four hours. That is recommendation of Caitanya Mahāprabhu.