To dream of a sunny day symbolises clarity and/or pleasantness. You are seeing things clearly. To dream of a gloomy or cloudy day signifies sadness. If you dream of a particular day, then you may need to look closely at that day for any significance. Consider the number associated with that day. A certain date could highlight a special anniversary, appointment or occasion.
To dream of the passing of a day indicates that you need to manage your time better and plot out your goals in a more deliberate manner.