Hey Aakash,
thanks for checking my problem.
I’ve set up a new WordPress installation without any other plugin and there it works.
I have no idee which other plugin caused this problem.
In the next few days I will check which Plugin caused the problem.
I’ve made this change to solve the problem for me:
In the file includes -> display.php in line 277 I changed this line
$countdown_time = new DateTime( $settings[ 'cdt_countdown' ], new DateTimeZone( $wp_timezone_name ) );
To this
$countdown_time = DateTime::createFromFormat('j. F Y H:i', $settings[ 'cdt_countdown' ]);
But I guess it will only work when you have the same Datetime format like me (i.e. 7. Dezember 2021 00:00) in the Datepicker.
Best regards,
Marius