Add or subtract time durations. Convert between hours, minutes, and seconds. Calculate total time from multiple entries.
Adding time requires handling overflow: seconds overflow into minutes (60 seconds = 1 minute), and minutes overflow into hours (60 minutes = 1 hour). For example: 2:45:30 + 1:30:45 = 4:16:15 (the 75 seconds overflow to 1 minute 15 seconds, then 76 minutes overflow to 1 hour 16 minutes).
Time unit conversions: 1 hour = 60 minutes = 3,600 seconds. 1 day = 24 hours = 1,440 minutes = 86,400 seconds. 1 week = 604,800 seconds. These are the base facts for all time arithmetic.
Common uses: calculating total work hours, adding meeting durations, figuring out elapsed time during travel, and computing overtime hours. For payroll calculations, convert total hours and minutes to decimal hours (e.g., 7 hours 30 minutes = 7.5 decimal hours).
Time arithmetic works in base 60: seconds and minutes roll over at 60, hours at 24. To add durations, sum each unit and carry overflow upward; to subtract, borrow downward.
Adding 2 h 45 min and 1 h 38 min: minutes total 83, which is 1 h 23 min, so the result is 4 h 23 min. Subtracting 1 h 50 min from 3 h 15 min: borrow one hour to get 2 h 75 min, minus 1 h 50 min leaves 1 h 25 min.
How do decimal hours work? Payroll systems often use decimals: 7.5 hours is 7 h 30 min. Divide minutes by 60 to convert (25 min = 0.42 h).
Time zones and DST? When events cross a daylight-saving change, wall-clock arithmetic can be off by an hour — compute in UTC for accuracy.