diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -3290,7 +3290,6 @@
     'phabricator_format_local_time' => 'view/viewutils.php',
     'phabricator_relative_date' => 'view/viewutils.php',
     'phabricator_time' => 'view/viewutils.php',
-    'phabricator_time_format' => 'view/viewutils.php',
     'phid_get_subtype' => 'applications/phid/utils.php',
     'phid_get_type' => 'applications/phid/utils.php',
     'phid_group_by_type' => 'applications/phid/utils.php',
diff --git a/src/applications/people/storage/PhabricatorUser.php b/src/applications/people/storage/PhabricatorUser.php
--- a/src/applications/people/storage/PhabricatorUser.php
+++ b/src/applications/people/storage/PhabricatorUser.php
@@ -738,6 +738,41 @@
     return new DateTimeZone($this->getTimezoneIdentifier());
   }
 
+  public function getPreference($key) {
+    $preferences = $this->loadPreferences();
+
+    // TODO: After T4103 and T7707 this should eventually be pushed down the
+    // stack into modular preference definitions and role profiles. This is
+    // just fixing T8601 and mildly anticipating those changes.
+    $value = $preferences->getPreference($key);
+
+    $allowed_values = null;
+    switch ($key) {
+      case PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT:
+        $allowed_values = array(
+          'g:i A',
+          'H:i',
+        );
+        break;
+      case PhabricatorUserPreferences::PREFERENCE_DATE_FORMAT:
+        $allowed_values = array(
+          'Y-m-d',
+          'n/j/Y',
+          'd-m-Y',
+        );
+        break;
+    }
+
+    if ($allowed_values !== null) {
+      $allowed_values = array_fuse($allowed_values);
+      if (empty($allowed_values[$value])) {
+        $value = head($allowed_values);
+      }
+    }
+
+    return $value;
+  }
+
   public function __toString() {
     return $this->getUsername();
   }
diff --git a/src/view/form/control/AphrontFormDateControl.php b/src/view/form/control/AphrontFormDateControl.php
--- a/src/view/form/control/AphrontFormDateControl.php
+++ b/src/view/form/control/AphrontFormDateControl.php
@@ -137,19 +137,13 @@
   }
 
   private function getTimeFormat() {
-    $viewer = $this->getUser();
-    $preferences = $viewer->loadPreferences();
-    $pref_time_format = PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT;
-
-    return $preferences->getPreference($pref_time_format, 'g:i A');
+    return $this->getUser()
+      ->getPreference(PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT);
   }
 
   private function getDateFormat() {
-    $viewer = $this->getUser();
-    $preferences = $viewer->loadPreferences();
-    $pref_date_format = PhabricatorUserPreferences::PREFERENCE_DATE_FORMAT;
-
-    return $preferences->getPreference($pref_date_format, 'Y-m-d');
+    return $this->getUser()
+      ->getPreference(PhabricatorUserPreferences::PREFERENCE_DATE_FORMAT);
   }
 
   private function getTimeInputValue() {
diff --git a/src/view/form/control/AphrontFormDateControlValue.php b/src/view/form/control/AphrontFormDateControlValue.php
--- a/src/view/form/control/AphrontFormDateControlValue.php
+++ b/src/view/form/control/AphrontFormDateControlValue.php
@@ -10,7 +10,6 @@
   private $zone;
   private $optional;
 
-
   public function getValueDate() {
     return $this->valueDate;
   }
@@ -56,6 +55,10 @@
     return $this->optional;
   }
 
+  public function getViewer() {
+    return $this->viewer;
+  }
+
   public static function newFromParts(
     PhabricatorUser $viewer,
     $year,
@@ -71,8 +74,7 @@
         $year,
         $month,
         $day,
-        coalesce($time, '12:00 AM'),
-        $value);
+        coalesce($time, '12:00 AM'));
     $value->valueEnabled = $enabled;
 
     return $value;
@@ -85,8 +87,7 @@
     list($value->valueDate, $value->valueTime) =
       $value->getFormattedDateFromDate(
         $request->getStr($key.'_d'),
-        $request->getStr($key.'_t'),
-        $value);
+        $request->getStr($key.'_t'));
 
     $value->valueEnabled = $request->getStr($key.'_e');
     return $value;
@@ -108,8 +109,7 @@
         $year,
         $month,
         $day,
-        $time,
-        $value);
+        $time);
 
     return $value;
   }
@@ -123,8 +123,7 @@
     list($value->valueDate, $value->valueTime) =
       $value->getFormattedDateFromDate(
         idx($dictionary, 'd'),
-        idx($dictionary, 't'),
-        $value);
+        idx($dictionary, 't'));
 
     $value->valueEnabled = idx($dictionary, 'e');
 
@@ -205,29 +204,25 @@
   }
 
   private function getTimeFormat() {
-    $preferences = $this->viewer->loadPreferences();
-    $pref_time_format = PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT;
-
-    return $preferences->getPreference($pref_time_format, 'g:i A');
+    return $this->getViewer()
+      ->getPreference(PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT);
   }
 
   private function getDateFormat() {
-    $preferences = $this->viewer->loadPreferences();
-    $pref_date_format = PhabricatorUserPreferences::PREFERENCE_DATE_FORMAT;
-
-    return $preferences->getPreference($pref_date_format, 'Y-m-d');
+    return $this->getViewer()
+      ->getPreference(PhabricatorUserPreferences::PREFERENCE_DATE_FORMAT);
   }
 
-  private function getFormattedDateFromDate($date, $time, $value) {
+  private function getFormattedDateFromDate($date, $time) {
     $original_input = $date;
-    $zone = $value->getTimezone();
-    $separator = $value->getFormatSeparator();
+    $zone = $this->getTimezone();
+    $separator = $this->getFormatSeparator();
     $parts = preg_split('@[,./:-]@', $date);
     $date = implode($separator, $parts);
     $date = id(new DateTime($date, $zone));
 
     if ($date) {
-      $date = $date->format($value->getDateFormat());
+      $date = $date->format($this->getDateFormat());
     } else {
       $date = $original_input;
     }
@@ -235,8 +230,8 @@
     $date = id(new DateTime("{$date} {$time}", $zone));
 
     return array(
-      $date->format($value->getDateFormat()),
-      $date->format($value->getTimeFormat()),
+      $date->format($this->getDateFormat()),
+      $date->format($this->getTimeFormat()),
     );
   }
 
@@ -244,14 +239,14 @@
     $year,
     $month,
     $day,
-    $time,
-    $value) {
-    $zone = $value->getTimezone();
+    $time) {
+
+    $zone = $this->getTimezone();
     $date_time = id(new DateTime("{$year}-{$month}-{$day} {$time}", $zone));
 
     return array(
-      $date_time->format($value->getDateFormat()),
-      $date_time->format($value->getTimeFormat()),
+      $date_time->format($this->getDateFormat()),
+      $date_time->format($this->getTimeFormat()),
     );
   }
 
diff --git a/src/view/phui/calendar/PHUICalendarListView.php b/src/view/phui/calendar/PHUICalendarListView.php
--- a/src/view/phui/calendar/PHUICalendarListView.php
+++ b/src/view/phui/calendar/PHUICalendarListView.php
@@ -141,11 +141,8 @@
   }
 
   private function getEventTooltip(AphrontCalendarEventView $event) {
-    $viewer = $this->getUser();
-    $preferences = $viewer->loadPreferences();
-    $time_pref = $preferences->getPreference(
-      PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT,
-      'g:i A');
+    $time_pref = $this->getUser()
+      ->getPreference(PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT);
 
     Javelin::initBehavior('phabricator-tooltips');
 
diff --git a/src/view/viewutils.php b/src/view/viewutils.php
--- a/src/view/viewutils.php
+++ b/src/view/viewutils.php
@@ -31,32 +31,21 @@
 }
 
 function phabricator_time($epoch, $user) {
+  $time_key = PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT;
   return phabricator_format_local_time(
     $epoch,
     $user,
-    phabricator_time_format($user));
+    $user->getPreference($time_key));
 }
 
 function phabricator_datetime($epoch, $user) {
+  $time_key = PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT;
   return phabricator_format_local_time(
     $epoch,
     $user,
     pht('%s, %s',
       phutil_date_format($epoch),
-      phabricator_time_format($user)));
-}
-
-function phabricator_time_format($user) {
-  $prefs = $user->loadPreferences();
-
-  $pref = $prefs->getPreference(
-    PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT);
-
-  if (strlen($pref)) {
-    return $pref;
-  }
-
-  return pht('g:i A');
+      $user->getPreference($time_key)));
 }
 
 /**