The aim of this study is to understand students¡¦ solutions (to problems related to time, time interval, and time unit conversion) and to analyze their common errors and possible causes. Students¡¦ problem-solving strategies and error types were also categorized and used as a reference for improvement in teaching and a scaffold for supporting students' learning. Findings in this research were three: 1. Distinction between time and interval. Students were performing better in the concept of interval than in the concept of time. They also performed well in total time consumed and in daily life problems such as clock time. However, problems with longer text description would make it harder for students to do problem solving in the concept of time and interval. 2. Problem-solving types. The problem-solving types ranked by the frequency are: (1) processing larger units first; (2) converting time from high scale to low scale and vice-versa; (3) using fractions; (4) using decimals; and (5) using addition. 3. Error types: The error types presented by students in solving time-related problems include: (1) interference of the decimal; (2) interference between non-decimal time conversion systems; (3) insufficient knowledge about division; (4) unclear concept about high and low scales of time; (5) incorrect calculation; (6) influence of the clock dial structure; (7) incorrect problem-solving strategy; (8) misjudgment of keywords; and (9) ignorance of problem conditions.