這四個與時間有關的片語，意思或相同或相近、不能全部等量齊觀，而它們的用法也有差異，使用上亦要小心！
Day after day 意為「日復一日；一連好幾天；每天」，尤指令人厭煩或不快的重複或連續的情況或行為，如 If you do the same things day after day, you will get bored. (如果你日復一日地做同樣的事，你會感到厭煩)；I think of my hometown day after day. (我每天思念著故鄉)。其他時間詞也可以這樣用，如 year after year, month after month, night after night 等。
Day and night 意為「日以繼夜；夜以繼日；日日夜夜；日夜不停地」，亦可用 night and day 來表示，如 His father worked day and night and eventually fell ill. (他父親日以繼夜地工作，終於病倒了)；I think of her night and day. (我日夜思念著她)。
Day by day 意為「一天天地；漸漸地」，如 My mother is getting better day by day. (我母親的健康狀況逐漸好轉)；My little granddaughter grows prettier day by day. (我的小孫女一天比一天漂亮)。其他時間詞也可以這樣用，如 year by year, month by month, week by week, hour by hour，但卻沒有 night by night 的說法或用法。
Day in, day out 與 day after day 是同義詞，有時寫成 day in day out，如 If we eat the same food day in day out, it isn’t surprising we get bored. (如果我們每天吃同樣的食物，我們會感到厭煩，自是不足為奇)；It went on raining day in, day out. (雨一連下了好幾天)。其他時間詞，尤其是表示較長時間的詞，也可以這樣用，如 year in, year out, month in, month out, week in, week out, night in, night out，但 hours, minutes 和 seconds 則不可以這樣用。