Ruminants have evolved to ruminate mostly over- night and graze during day. As such, rumen fermentation, post-rumen nutrient assimilation and peripheral metabolism have 24-h patterns. These evolutionary rhythms in eating behavior and metabolism have led to annual, seasonal, and circadian rhythms in ruminant endocrinology. Such natural patterns have encountered dramatic shifts in productivity in the last few decades. For optimum nutrient use and animal health, securing a synchrony between external cues and ruminant internal conditions is essential. Most recent discoveriess suggest alterations in post-prandial intake patterns of non-grazing lactating cows by altered feeding time. Eating rate and feed intake within the first 3 h after feeding have been increased by evening instead of morning feeding. As a result, postprandial patterns in rumen fermentation and peripheral blood levels of metabolites and hormones have been altered. These findings and insights establish a chronological nature for intake regulation in modern ruminants. Feeding time is a major external cue that affects eating extent, rate and efficiency in ruminants. Time of feeding requires special consideration and more mechanistic evaluations for animals and humans.