Before the day is over or before the day ends ( the same )

Do you mean "before the day of"? If so that means something must have been completed or something has been done before the day being spoken about starts. (i.e. "Please have this done before the day of".) "Before the day is over" whatever you wish to have completed must be done by the end of the day being spoken about ("Please have this done before the day is over"). As an example: the day in question is June 4th. "Please get this done before the day of (June 4th)". You must have completed it before June 4th starts. "Please get this done before June 4th is over". You must have completed it by the time June 4th ends. If you need more clarification let me know.