白天=daytime，夜晚≠nighttime
可以看出，英语是一种不合逻辑的语言。
daytime（白天）是一个词:night-time或night time（夜晚）则不是一个词。需要加连字符或者空格。
例句：
during the daytime he has to work and at night he must take care of their children.
他白天需要工作，晚上还要照顾孩子。
the government announced a night-time curfew.
政府宣布实行宵禁。
很多时候还可以不加“time”
例句：
during the day he has to work.
他白天需要工作。
these days everyone is working both day and night to finish the job on time.
这几天大家都在日以继夜地忙着完成任务。