In Excel time if time is mentioned in hh:mm format (12:40 AM). Here if you need to add minutes to this time, a simple formula can be used.
Add minutes to time
Simply divide the minutes by 1440 and add to time in hh:mm format.
Another way is to convert minutes to format hh:mm by using formula TIME(hours, minutes, seconds)
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This guide applies Excel 2010 you can test on other excel versions Add minutes to time