When elapsed time spans more than one hour, students add hours and minutes separately. For example, from 2:15 PM to 5:30 PM is 3 hours and 15 minutes. Number lines and timelines help visualize the passage of time.
You already know how to find elapsed time when the start and end are within the same hour. If something starts at 2:10 and ends at 2:45, you count up by minutes: 35 minutes have passed. That strategy works perfectly inside one hour. But what do you do when time crosses the hour mark — or spans several hours?
The key idea is to break the problem into steps, using whole-hour marks as natural stopping points. Suppose you want to find the elapsed time from 2:15 PM to 5:30 PM. Rather than calculating it all at once, use the clock's structure: from 2:15 to 3:00 is 45 minutes (completing the current hour); from 3:00 to 5:00 is exactly 2 whole hours; from 5:00 to 5:30 is 30 more minutes. Add those pieces: 45 minutes + 2 hours + 30 minutes. Combining: 2 hours and 75 minutes — but 75 minutes is 1 hour and 15 minutes, so the total is 3 hours and 15 minutes. You can also count whole hours directly (2:15 to 5:15 = exactly 3 hours, then 15 more minutes to 5:30), which is often even faster.
A number line makes this visual. Place the start time on the left and the end time on the right. Draw labeled jumps for whole hours, then a smaller jump for the remaining minutes. The total elapsed time is the sum of all your jumps. This builds directly on your experience using number lines to add — the same tool, now applied to time instead of whole numbers.
The most important thing to watch: time does not use base-ten grouping — there are 60 minutes in an hour, not 100. If your calculation produces 75 minutes, you must regroup: 75 minutes = 1 hour and 15 minutes (since 75 = 60 + 15). Always check whether your minutes total reaches 60 or more, and convert if so. Missing this regrouping is the most common source of errors in elapsed-time problems, and checking it takes only a moment.