Letters of recommendation are testimonials by professors, past employers, or extracurricular advisors regarding your abilities, skills, and character.
Make your ask for a letter of recommendation well ahead of time, at least 3 weeks before it's due. You wouldn’t stay up all night fourth week Tuesday writing your final paper, would you? (Don’t answer that.)
The point is, a letter will only benefit you if you give faculty and staff enough time to write you a quality letter.
What are references for?
Referencesare people in positions of authority who have direct knowledge of your work or study habits, such as former supervisors, professors, advisors, or mentors. If an application asks for references, you need only submit a list of names and contact information, not a letter from each individual on your list.
Before submitting your reference list, contact your references and ask if they are willing to serve as a reference and send them an updated copy of your resume to refresh their memory. Employers may call all, none, or only a couple of people from your list, but still ask for your references if you can list them and give them a heads up when you've submitted an application.
Know the difference between “references” and “letters of recommendation” before you ask someone to write a letter for you.