The display of date/time values in DIAdem is controlled by a global variable named 'TimeFormat'. You can view and change the format by visiting: menu 'Settings', option 'DIAdem Settings', 'General', 'General', 'Time Format:'.
You didn't indicate where in DIAdem you were viewing the date/time values. In the Data Portal, the display is controlled by 'Time Format'. In View, you can change the display in a Channel Table, and of course in a chart plot. In Report, you can modify the default format of date/time values in a chart too.
Make sure those values are actually a data type of Date/Time (DIAdem calls it 'Time"), and not a string. In the Data Portal, look a the channel property "Other~Display format". It will be 'Text', 'Numeric', or 'Time'. If not the desired format ('Time'), then revise your CSV DataPlugin.