Due to the phenomenon of the expertise reversal effect, different teaching strategies may have opposite effects on novice and expert learners. Therefore, it is necessary to consider providing differential guidance information based on the operator’s proficiency level. This study aimed to investigate the impact of operator proficiency levels on the distribution of assembly operation times in manual assembly tasks. A continuous assembly experiment was designed to collect assembly time distribution data from operators with different proficiency levels. Results indicated that operators of different proficiency levels significantly affected the time distribution of assembly stages and the frequency of errors. As proficiency increased, the time taken for each operational stage decreased gradually, accompanied by a reduction in error occurrences. By analyzing these time distribution data, important references can be provided for the future construction of a proficiency grading system, which can in turn lay the foundation for the design of a differential assistance assembly system based on user proficiency.