Charles Ellicott Commentary John 6:66

"Upon this many of his disciples went back, and walked no more with him." — John 6:66 (ASV)

From that time.—The addition of the word “time” has given a definite and questionable meaning to the Greek, which is indefinite. “From that” probably means on that account, because of the words He had spoken. The actual departure was the result of the teaching, which tested their faith and found it wanting, and was at that time, not gradually from that time onwards. (Compare to the Note on John 19:12.)

Many of his disciples.—Co-extensive with the same term in John 6:60.