Pure devotional service is so spiritually relishable that a devotee becomes automatically uninterested in material enjoyment. That is the sign of perfection in progressive devotional service. A pure devotee continuously remembers the lotus feet of the Lord Sri Krishna and does not forget Him even for a moment, not even in exchange for all the opulence of the three worlds.
By performing congregational chanting of the Hare Krishna mantra, one can destroy the sinful condition of material existence, purify the unclean heart and awaken all varieties of devotional service.
Chaitanya Caritamrta on Antya Lila 20.13
Of the nine processes of devotional service, the most important is to always chant the holy name of the Lord. If one does so, avoiding the ten kinds of offenses, one very easily obtained the most valuable love of Godhead.
Chaitanya Caritamrta Antya Lila 4.71
A devotee doing sense gratification out of material conditionings, if keeps on listening to pure devotees, soon becomes disgusted of sense gratification and gives it up, and so attains the pure devotion to krishna.
Bhakti is an effort that produces bliss and work is that effort which produces exhaustion.
One may require 8 hours of sleep but he/ she is still doing uttama bhakti if the remaining 16 hours are spent serving Lord Krishna favorably.