A day in a dream represents a period of time in real life, not necessarily a 24-hour period.
Something that happens over the course of a day in a dream can symbolize something that is taking place over a period of time in your life. Something that is going to happen in a day in a dream can represent something that is going to take place in the future.
If you dream that something is going to take place over the course of a day, you could be frustrated about something that is going on in your life. Your dream is telling you that you must be patient; that eventually things will change.
Dreaming that something will not happen until the next day can mean that you are feeling impatient about something. Alternatively, your dream can mean that you feel that something is happening too quickly.
If you dream of the passage from night to day, you may have experienced a bad situation, but things now seem to be getting better.
If you dream that it was day but that night is coming, you could be beginning to feel depressed.