Add And Customize Date And Time Formats. See belowfor more information about available standard format patterns and how to construct a custom format string. The easiest way to set a custom date format in Excel is to start from an existing format close to what you want.
Use the Short name drop-down menu to select the date format you want to see in the Taskbar. The custom date format you entered displays in the Short date box in the Example section. After that click Custom and make changes to the format displayed in the Type box.
For example you can combine the General Date and Long Time formats as.
Select Change date and time in the Date and Time window. Do the right-click and select Format Cells. Select Change date and time in the Date and Time window. The D standard format specifier represents a custom date and time format string that is defined by the current DateTimeFormatInfoLongDatePattern property.