diff --git a/lib/function/study_calendar_controller.dart b/lib/function/study_calendar_controller.dart
index 7293256..d9e7291 100644
--- a/lib/function/study_calendar_controller.dart
+++ b/lib/function/study_calendar_controller.dart
@@ -13,6 +13,7 @@ class StudyCalendarController extends ChangeNotifier {
   bool _isBusy = false;
   int _currentStreak = 0;
   int _longestStreak = 0;
+  int _attendanceThresholdSeconds = 3600;
   Set<String> _studiedDates = {};
   Map<String, dynamic> _events = {}; // date -> {title, description}
   DateTime _visibleMonth = DateTime.now();
@@ -22,6 +23,7 @@ class StudyCalendarController extends ChangeNotifier {
   bool get isBusy => _isBusy;
   int get currentStreak => _currentStreak;
   int get longestStreak => _longestStreak;
+  int get attendanceThresholdSeconds => _attendanceThresholdSeconds;
   Set<String> get studiedDates => _studiedDates;
   Map<String, dynamic> get events => _events;
   DateTime get visibleMonth => _visibleMonth;
@@ -68,6 +70,8 @@ class StudyCalendarController extends ChangeNotifier {
         final data = jsonDecode(utf8.decode(response.bodyBytes));
         _currentStreak = (data['currentStreak'] as num?)?.toInt() ?? 0;
         _longestStreak = (data['longestStreak'] as num?)?.toInt() ?? 0;
+        _attendanceThresholdSeconds =
+            (data['attendanceThresholdSeconds'] as num?)?.toInt() ?? 3600;
         _studiedDates = ((data['studiedDates'] as List<dynamic>?) ?? [])
             .map((d) => d.toString())
             .toSet();
diff --git a/lib/ui/group_detail_screen.dart b/lib/ui/group_detail_screen.dart
index a8d5148..573109b 100644
--- a/lib/ui/group_detail_screen.dart
+++ b/lib/ui/group_detail_screen.dart
@@ -209,9 +209,12 @@ class _GroupDetailScreenState extends State<GroupDetailScreen> {
   }
 
   String _formatMinutes(int seconds) {
-    final m = seconds ~/ 60;
-    if (m < 60) return '$m분';
-    return '${m ~/ 60}시간 ${m % 60}분';
+    final h = seconds ~/ 3600;
+    final m = (seconds % 3600) ~/ 60;
+    final s = seconds % 60;
+    if (h > 0) return '$h시간 $m분';
+    if (m > 0) return '$m분 $s초';
+    return '$s초';
   }
 
   void _openTimer() {
@@ -412,6 +415,14 @@ class _GroupDetailScreenState extends State<GroupDetailScreen> {
                           ),
                         ],
                       ),
+                      const SizedBox(height: 4),
+                      Text(
+                        '1시간 이상 공부해야 출석으로 표시돼요.',
+                        style: TextStyle(
+                          fontSize: 11.5,
+                          color: Colors.grey[500],
+                        ),
+                      ),
                       const SizedBox(height: 10),
                       GridView.builder(
                         shrinkWrap: true,
diff --git a/lib/ui/study_calendar_screen.dart b/lib/ui/study_calendar_screen.dart
index 5856a54..1f5463a 100644
--- a/lib/ui/study_calendar_screen.dart
+++ b/lib/ui/study_calendar_screen.dart
@@ -234,6 +234,17 @@ class _StudyCalendarScreenState extends State<StudyCalendarScreen> {
                         ),
                       ],
                     ),
+                    const SizedBox(height: 8),
+                    Center(
+                      child: Text(
+                        '하루 ${_controller.attendanceThresholdSeconds ~/ 60}분 '
+                        '이상 공부해야 그날 출석으로 인정돼요.',
+                        style: TextStyle(
+                          fontSize: 11.5,
+                          color: Colors.grey[500],
+                        ),
+                      ),
+                    ),
                     const SizedBox(height: 20),
                     Row(
                       mainAxisAlignment: MainAxisAlignment.spaceBetween,
diff --git a/lib/ui/study_ranking_screen.dart b/lib/ui/study_ranking_screen.dart
index 592f48e..3b81fad 100644
--- a/lib/ui/study_ranking_screen.dart
+++ b/lib/ui/study_ranking_screen.dart
@@ -38,8 +38,10 @@ class _StudyRankingScreenState extends State<StudyRankingScreen> {
   String _formatHM(int totalSeconds) {
     final h = totalSeconds ~/ 3600;
     final m = (totalSeconds % 3600) ~/ 60;
-    if (h > 0) return '$h시간 $m분';
-    return '$m분';
+    final s = totalSeconds % 60;
+    if (h > 0) return '$h시간 $m분 $s초';
+    if (m > 0) return '$m분 $s초';
+    return '$s초';
   }
 
   Color? _rankColor(int rank) {
diff --git a/lib/ui/study_timer_screen.dart b/lib/ui/study_timer_screen.dart
index b2438d9..f368634 100644
--- a/lib/ui/study_timer_screen.dart
+++ b/lib/ui/study_timer_screen.dart
@@ -114,8 +114,10 @@ class _StudyTimerScreenState extends State<StudyTimerScreen>
   String _formatHM(int totalSeconds) {
     final h = totalSeconds ~/ 3600;
     final m = (totalSeconds % 3600) ~/ 60;
-    if (h > 0) return '$h시간 $m분';
-    return '$m분';
+    final s = totalSeconds % 60;
+    if (h > 0) return '$h시간 $m분 $s초';
+    if (m > 0) return '$m분 $s초';
+    return '$s초';
   }
 
   Future<void> _runAction(