The duration of a small mid-term exam in the United States typically ranges from 30 minutes to 2 hours, depending on the subject matter and the institution's policies. This time frame allows students to demonstrate their understanding of the course material without overwhelming them with an excessively long exam. According to a survey conducted by the National Center for Education Statistics (NCES), the average duration of a mid-term exam in higher education institutions is approximately 1.5 hours. This duration is designed to ensure that students can effectively showcase their knowledge and skills while also providing them with a reasonable amount of time to reflect on their answers.