dhyāyantam ekam āsīnaḿ
puruṣaḿ prakṛteḥ param
śuśrūṣantaḿ gurūn kvāpi
kāmair bhogaiḥ saparyayā
dhyayantam -- meditating; ekam -- alone; asinam -- sitting; purusham -- on the Supreme Personality of Godhead; prakriteh -- to material nature; param -- transcendental; susrushantam -- rendering menial service; gurun -- to His elders; kva api -- somewhere; kamaih -- desirable; bhogaih -- with objects of enjoyment; saparyaya -- and with worship.
Srila Prabhupada comments, "Meditation, as recommended in authorized scripture, is meant for concentrating one's mind on the Supreme Personality of Godhead, Vishnu. Lord Krishna is Himself the original Vishnu, but because He played the part of a human being, He taught us definitely by His personal behavior what is meant by meditation."
This activity of meditation indicates the brahma-muhurta, the early morning hours before sunrise.