Facing install warning every time in Drupal 8.2.5

I am using it successfully but what about the long red texts on every new Drupal 8 install?

The new Drupal 8.2.5 install succeeded with
"One translation file imported. 1448 translations were added, 0 translations were updated and 0 translations were removed.
बधाई हो, आपने Drupal को स्थापित कर लिया !"

AND the long red texts too -

Warning: DateTime::createFromFormat(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in Symfony\Component\HttpFoundation\Response->sendHeaders() (line 331 of vendor/symfony/http-foundation/Response.php).
Symfony\Component\HttpFoundation\Response->sendHeaders() (Line: 371)
Symfony\Component\HttpFoundation\Response->send() (Line: 637)
install_run_task(Array, Array) (Line: 538)
install_run_tasks(Array) (Line: 115)
install_drupal(Object) (Line: 44)
Warning: DateTime::createFromFormat(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in Symfony\Component\HttpFoundation\Response->sendHeaders() (line 331 of vendor/symfony/http-foundation/Response.php).
Symfony\Component\HttpFoundation\Response->sendHeaders() (Line: 371)
Symfony\Component\HttpFoundation\Response->send() (Line: 637)
install_run_task(Array, Array) (Line: 538)
install_run_tasks(Array) (Line: 115)
install_drupal(Object) (Line: 44)