There is a comment that states that there is no difference between the single recitation and reciting ten times, but this comment is appropriate only for one's last moments ("Kurodani Sho'nin Gotoroku" - "Nenbutsu Ojo Yogisho").
一念でも十念でも優劣は無いという記述があるが、これはあくまでも最後の時のこととしている(『黒谷上人語灯録』-念佛往生容義抄)。