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
@@ -141,6 +141,12 @@
   }
 
   private function getEventTooltip(AphrontCalendarEventView $event) {
+    $viewer = $this->getUser();
+    $preferences = $viewer->loadPreferences();
+    $time_pref = $preferences->getPreference(
+      PhabricatorUserPreferences::PREFERENCE_TIME_FORMAT,
+      'g:i A');
+
     Javelin::initBehavior('phabricator-tooltips');
 
     $start = id(AphrontFormDateControlValue::newFromEpoch(
@@ -166,13 +172,13 @@
       if ($start->getValueDate() == $end->getValueDate()) {
         $tip = pht(
           '%s - %s',
-          $start->getValueAsFormat('g:i A'),
-          $end->getValueAsFormat('g:i A'));
+          $start->getValueAsFormat($time_pref),
+          $end->getValueAsFormat($time_pref));
       } else {
         $tip = pht(
           '%s - %s',
-          $start->getValueAsFormat('M j, Y, g:i A'),
-          $end->getValueAsFormat('M j, Y, g:i A'));
+          $start->getValueAsFormat('M j, Y, '.$time_pref),
+          $end->getValueAsFormat('M j, Y, '.$time_pref));
       }
     }
     return $tip;