Elapsed time, and all time concepts, are tricky to teach. Students seem to either “get it” or not, and there doesn’t seem to be a correlation between proficiency at other mathematical skills and the ability to calculate time. No matter the reason, elapsed time can be especially difficult to master. Here are some tips and favorite strategies for teaching elapsed time.
https://www.scholastic.com/teachers/blog-posts/meghan-everette/teaching-elapsed-time-strategies-work/