Time Calculator

Because it can fall across a daylight-saving change. Twenty-four hours is an elapsed-time span; a calendar day is not always 24 hours long. In a spring-forward week a day is 23 hours and in a fall-back week it is 25, so adding 24 hours shifts the wall clock by an hour. If you want the same clock time on the next day, add 1 day rather than 24 hours.

Not reliably. The date-time inputs the browser gives you here carry hours and minutes but not seconds, so the Between result is always a whole number of minutes. The Totals line still shows the span in seconds, but that number is only the minutes multiplied out.

It restates the same duration in three flat units: the whole span expressed as hours, as minutes, and as seconds. A gap of 1 day 2 hours reads as 26 hours, 1560 minutes, and 93600 seconds. It is there because timesheets and billing systems usually want one flat unit rather than a broken-down duration.

No. It takes one base time and one duration, or two timestamps. If you are totalling a week of timesheet entries you will need to sum them yourself, or use a spreadsheet, since there is no list mode here.

No. Every hour counts, including nights, weekends, and public holidays. If you need to know how many business days lie between two dates, this is the wrong tool; it measures raw elapsed time only.