There is no option to display Current Date and Time in WordPress powered site. But this can be easily achieved by inserting simple php functions in your theme file:
Time and Date format can also be changed as per your convenience. There is a guide here: Formatting Date and Time
Now, to display this time and date as a widget, you need to few lines of codes or you can rely upon this simplest plugin: Current Date & Time Widget
Don’t worry! although the plugin has not been updated for many years, still it works perfectly.