diff --git a/lib/Config/Menu.php b/lib/Config/Menu.php
index c6507ab5d9..f3676c52a7 100644
--- a/lib/Config/Menu.php
+++ b/lib/Config/Menu.php
@@ -404,7 +404,7 @@ class Menu {
     $data['roles']['mailpoet_all'] = __('In any WordPress role');
 
     $date_time = new DateTime();
-    $data['current_date'] = $date_time->getCurrentDate(DateTime::INTERNAL_DATE_FORMAT);
+    $data['current_date'] = $date_time->getCurrentDate(DateTime::DEFAULT_DATE_FORMAT);
     $data['current_time'] = $date_time->getCurrentTime();
     $data['schedule_time_of_day'] = $date_time->getTimeInterval(
       '00:00:00',
@@ -496,4 +496,4 @@ class Menu {
       ? (int)$listing_per_page
       : Listing\Handler::DEFAULT_LIMIT_PER_PAGE;
   }
-}
\ No newline at end of file
+}
diff --git a/lib/WP/DateTime.php b/lib/WP/DateTime.php
index b42bfbd6ec..2b0359f094 100644
--- a/lib/WP/DateTime.php
+++ b/lib/WP/DateTime.php
@@ -3,22 +3,22 @@ namespace MailPoet\WP;
 
 class DateTime {
 
-  const INTERNAL_DATE_FORMAT = 'Y-m-d';
-  const INTERNAL_TIME_FORMAT = 'H:i:s';
-  const INTERNAL_DATE_TIME_FORMAT = 'Y-m-d H:i:s';
+  const DEFAULT_DATE_FORMAT = 'Y-m-d';
+  const DEFAULT_TIME_FORMAT = 'H:i:s';
+  const DEFAULT_DATE_TIME_FORMAT = 'Y-m-d H:i:s';
 
   function __construct() {
   }
 
   function getTimeFormat() {
     $time_format = get_option('time_format');
-    if (empty($time_format)) $time_format = self::INTERNAL_TIME_FORMAT;
+    if (empty($time_format)) $time_format = self::DEFAULT_TIME_FORMAT;
     return $time_format;
   }
 
   function getDateFormat() {
     $date_format = get_option('date_format');
-    if (empty($date_format)) $date_format = self::INTERNAL_DATE_FORMAT;
+    if (empty($date_format)) $date_format = self::DEFAULT_DATE_FORMAT;
     return $date_format;
   }
 
@@ -32,15 +32,15 @@ class DateTime {
     return $this->getCurrentTime($format);
   }
 
-  function getTime($time, $format=false) {
+  function formatTime($timestamp, $format=false) {
     if (empty($format)) $format = $this->getTimeFormat();
 
-    return date($format, $time);
+    return date($format, $timestamp);
   }
 
   /**
    * Generates a list of time strings within an interval,
-   * formatted and mapped from INTERNAL_TIME_FORMAT to Wordpress time strings.
+   * formatted and mapped from DEFAULT_TIME_FORMAT to Wordpress time strings.
    */
   function getTimeInterval(
     $start_time='00:00:00',
@@ -49,15 +49,15 @@ class DateTime {
   ) {
     $steps = array();
 
-    $internal_time = $start_time;
-    $timestamp = strtotime($internal_time);
+    $formatted_time = $start_time;
+    $timestamp = strtotime($formatted_time);
 
     for ($step = 0; $step < $total_steps; $step += 1) {
-      $wordpress_time = $this->getTime($timestamp);
-      $steps[$internal_time] = $wordpress_time;
+      $formatted_time = $this->formatTime($timestamp, self::DEFAULT_TIME_FORMAT);
+      $label_time = $this->formatTime($timestamp);
+      $steps[$formatted_time] = $label_time;
 
       $timestamp = strtotime($time_step, $timestamp);
-      $internal_time = $this->getTime($timestamp, self::INTERNAL_TIME_FORMAT);
     }
 
     return $steps;
diff --git a/tests/_support/Helper/WordPress.php b/tests/_support/Helper/WordPress.php
new file mode 100644
index 0000000000..326dddd3fe
--- /dev/null
+++ b/tests/_support/Helper/WordPress.php
@@ -0,0 +1,35 @@
+<?php
+namespace Helper;
+// here you can define custom actions
+// all public methods declared in helper class will be available in $I
+
+class WordPress extends \Codeception\Module
+{
+  private static $functions_to_intercept = array();
+
+  static function interceptFunction($function_name, $callback) {
+    self::$functions_to_intercept[$function_name] = $callback;
+  }
+
+  static function releaseFunction($function_name) {
+    unset(self::$functions_to_intercept[$function_name]);
+  }
+
+  static function releaseAllFunctions() {
+    self::$functions_to_intercept = array();
+  }
+
+  static function getInterceptor($function_name) {
+    if (isset(self::$functions_to_intercept[$function_name]))
+      return self::$functions_to_intercept[$function_name];
+  }
+}
+
+// WP function overrides for \MailPoet namespace go here
+namespace MailPoet\WP;
+
+function get_option($key) {
+  if ($callback = \Helper\Wordpress::getInterceptor('get_option'))
+    return $callback($key);
+  return \get_option($key);
+}
diff --git a/tests/unit.suite.yml b/tests/unit.suite.yml
index 02dc9b1e0a..98a676a61e 100644
--- a/tests/unit.suite.yml
+++ b/tests/unit.suite.yml
@@ -6,4 +6,5 @@ class_name: UnitTester
 modules:
     enabled:
         - Asserts
-        - \Helper\Unit
\ No newline at end of file
+        - \Helper\Unit
+        - \Helper\WordPress
diff --git a/tests/unit/WP/DateTimeTest.php b/tests/unit/WP/DateTimeTest.php
new file mode 100644
index 0000000000..8eae9f9497
--- /dev/null
+++ b/tests/unit/WP/DateTimeTest.php
@@ -0,0 +1,82 @@
+<?php
+use \Helper\WordPress as WordPressHelper;
+use \MailPoet\WP\DateTime;
+
+class DateTimeTest extends MailPoetTest {
+  function _before() {
+    $this->date_time = new DateTime();
+  }
+
+  function testGetTimeFormat() {
+    WordPressHelper::interceptFunction('get_option', function($key) {
+      return 'H:i';
+    });
+    expect($this->date_time->getTimeFormat())->equals('H:i');
+
+    WordPressHelper::interceptFunction('get_option', function($key) {
+      return '';
+    });
+    expect($this->date_time->getTimeFormat())->equals('H:i:s');
+  }
+
+  function testGetDateFormat() {
+    WordPressHelper::interceptFunction('get_option', function($key) {
+      return 'm-d';
+    });
+    expect($this->date_time->getDateFormat())->equals('m-d');
+
+    WordPressHelper::interceptFunction('get_option', function($key) {
+      return '';
+    });
+    expect($this->date_time->getDateFormat())->equals('Y-m-d');
+  }
+
+  function testGetCurrentDate() {
+    expect($this->date_time->getCurrentDate("Y-m"))->equals(date("Y-m"));
+  }
+
+  function testGetCurrentTime() {
+    expect($this->date_time->getCurrentTime("i:s"))->regExp('/\d\d:\d\d/');
+  }
+
+  function testFormatTime() {
+    $timestamp = 1234567;
+    $format = "H:i:s";
+    expect($this->date_time->formatTime($timestamp, $format))->equals(date($format, $timestamp));
+  }
+
+  function testTimeInterval() {
+    $one_hour_interval = array_keys($this->date_time->getTimeInterval(
+      '00:00:00',
+      '+1 hour',
+      $total_steps=5
+    ));
+    $one_hour_expected = array(
+      '00:00:00', '01:00:00', '02:00:00', '03:00:00', '04:00:00');
+    expect($one_hour_interval)->equals($one_hour_expected);
+
+    $quarter_hour_interval = array_keys($this->date_time->getTimeInterval(
+      '00:00:00',
+      '+15 minute',
+      $total_steps=5
+    ));
+    $quarter_hour_expected = array(
+      '00:00:00', '00:15:00', '00:30:00', '00:45:00', '01:00:00',
+    );
+    expect($quarter_hour_interval)->equals($quarter_hour_expected);
+
+    $offset_start_time_interval = array_keys($this->date_time->getTimeInterval(
+      '03:00:00',
+      '+1 hour',
+      $total_steps=5
+    ));
+    $offset_start_time_expected = array(
+      '03:00:00', '04:00:00', '05:00:00', '06:00:00', '07:00:00',
+    );
+    expect($offset_start_time_interval)->equals($offset_start_time_expected);
+  }
+
+  function _afterStep() {
+    Wordpress::releaseAllFunctions();
+  }
+}