In the new Google sheets there\'s a way of formatting a number as a duration. Format -> Number -> Duration.
1 is formatted as 24:00:00
There is no need to use formulas for that, you can define your own custom formats.
Just go to Format -> Number -> More formats -> More date and time formats. It will open a window with several date and time formats to choose from. You can define your own as well, using the upper text area:
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