Please accept my humble obaisences
All glories to Srila Prabhupada
Yesterday one devotee from Gaudiya math justified his chanting 4 rounds with quotes from Srila Sridhara Swami and Govinda Maharaja his disciple.I do not know about their teachings in this matter.However I do know Srila Bhaktisiddhanta Prabhupada only had one standard :
One lahk minimum there is no compromise
Shrila Bhaktisiddhanta Sarasvati Thakura Prabhupada: "bhagavad-bhakta matrei pratyaha laksha-nama grahana karibena natuva vividha visaye asakta haiya bhagavad-seva karite asamartha haibena." The Lord continued-"Those who consider themselves devotees of the Lord must compulsorily chant 100,000 names of Krishna everyday otherwise they will gradually but surely become attached to varieties of sense-objects and thus become incapable to rendering any kind of service to the Lord."
lakshesvara vyatita gaura-bhaktira adarsa gaudiyajana kehai svikara karena na. "This is the precise reason why the real Gaudiya-bhaktas do not accept any other ideal (adarsa) in Gaura-bhakti or Krishna-bhakti except the of chanting 100,000 names of the maha-mantra daily.
Shrila Bhaktisiddhanta Sarasvati Thakura Prabhupada: adhapatita va adhapete gana eka-matra bhajana-sabda-vacya shri-nama-bhajane vimukhata-vasata laksha-nama grahana karibara parivarte anya bhajanera chalana korena, taddvara tahadera kona mangala haya na. "Those spiritual aspirants who are already fallen or will fall down from spiritual life in the future are averse to this sole means of deliverance called nama-bhajana, which is the worship of the sound incarnation of God in the form of chanting 100,000 names of the the Holy Names daily. Coming under the sway of their averseness to chant laksha-nama daily, they duplicitously invent (chalana) other means of devotional service (bhajana) to justify their not chanting 100,000 names daily but it is to be clearly understood that by this action they will not achieve anything auspicious (mangala) in their spiritual life."
16 rounds is Prabhupadas minimum standard 64 rounds is Lord Caitanyas standard,take it or leave it,