In this lesson, students learn how to add and subtract different units of time, including seconds, minutes, hours, days, months, and years. The key rule is to always start with the smallest unit, carrying over to the next bigger unit when the total exceeds its conversion factor, and borrowing from the next bigger unit when the smaller unit is not enough for subtraction. Conversion factors like 60 seconds = 1 minute, 60 minutes = 1 hour, 24 hours = 1 day, 30 days ≈ 1 month (approximate), and 12 months = 1 year are applied throughout. Students practice both direct calculations and real-life word problems, such as finding total travel times, comparing project durations, calculating age differences, and measuring homework time. The lesson emphasizes converting all time into the smallest unit for accuracy and then converting back to larger units for the final answer. This method ensures clarity, accuracy, and correct unit labeling in every solution.