LSDate

LSDate is a menu bar item which copies the current date and time onto the clipboard, or computes the difference between current date-time and selected date-time. Various formats supported, including custom formats. Use its system preference pane to specify settings: Select "Use Symbolic Names" to display the name of the type of menu item. Otherwise the actual date and time value will be displayed. Select "Include Date Only Items" or "Include Time Only Items" to optionally include menu items that display only the date or time, respectively.

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