Charles Spurgeon Commentary Mark 14:29-30

"But Peter said unto him, Although all shall be offended, yet will not I. And Jesus saith unto him, Verily I say unto thee, that thou to-day, [even] this night, before the cock crow twice, shalt deny me thrice." — Mark 14:29-30 (ASV)

But Peter said unto him, Although all shall be offended, yet will not I. And Jesus saith unto him, Verily I say unto thee, that this day, even in this night,

The day begins at sunset.