By the end of the day is a common phrase used to indicate the time frame for completing a task or reaching a goal. However, there are several synonyms that can be used to convey the same sense of urgency and priority. Some alternatives include by close of business, by day's end, before nightfall, by sundown, before the day is out, before the evening, by the stroke of midnight, by nightfall, and at the eleventh hour. Each of these phrases offers a slightly different emphasis on the time frame and urgency of the task at hand, allowing the speaker to choose the most appropriate synonym for their specific context.