Chore/revisit issue 81

lib/src/iteration/frequency_interval.dart

@@ -131,7 +131,7 @@ extension _FrequencyIntervalCalculation on DateTime {
 
     while (true) {
       final minutes = seconds ~/ Duration.secondsPerMinute;
-      final secondsWithoutMinutes = minutes % Duration.secondsPerMinute;
+      final secondsWithoutMinutes = seconds % Duration.secondsPerMinute;
       if (minutes > 0) {
         newValue = newValue._addMinutes(
           minutes,

lib/src/iteration/iteration.dart

@@ -31,15 +31,16 @@ Iterable<DateTime> getRecurrenceRuleInstances(
   var count = rrule.count;
 
   var currentStart = start;
-  if (rrule.actualInterval == 1 &&
-      count == null &&
-      after != null &&
-      rrule.frequency <= Frequency.daily) {
+
+  if (rrule.actualInterval == 1 && count == null && after != null) {
     // Shortcut for not calculating unnecessary recurrences.
-    currentStart = after;
+    currentStart = after.copyWith(
+      millisecond: start.millisecond,
+      microsecond: start.microsecond,
+    );
   }
 
-  var timeSet = makeTimeSet(rrule, start.timeOfDay);
+  var timeSet = makeTimeSet(rrule, currentStart.timeOfDay);
 
   while (true) {
     final dateSet = makeDateSet(rrule, currentStart.atStartOfDay);

test/recurrence_rule_test.dart

@@ -322,13 +322,33 @@ void main() {
       equals([DateTime.utc(2024, 2, 25), DateTime.utc(2024, 3, 10)]),
     );
   });
-  test('#81: Occurrence skipped when using after with frequency > daily', () {
-    final rule = RecurrenceRule.fromString('RRULE:FREQ=HOURLY;INTERVAL=1');
-    final start = DateTime.utc(2026, 01, 05, 18, 50, 00);
-    final after = DateTime.utc(2026, 01, 05, 19, 24, 54, 548180);
-    expect(
-      rule.getInstances(start: start, after: after).first,
-      equals(DateTime.utc(2026, 01, 05, 19, 50, 00)),
-    );
+  group('#81: Occurrence skipped when using after with frequency > daily', () {
+    test('(HOURLY)', () {
+      final rule = RecurrenceRule.fromString('RRULE:FREQ=HOURLY;INTERVAL=1');
+      final start = DateTime.utc(2026, 01, 05, 18, 50, 00);
+      final after = DateTime.utc(2026, 01, 05, 19, 24, 54, 548, 180);
+      expect(
+        rule.getInstances(start: start, after: after).first,
+        equals(DateTime.utc(2026, 01, 05, 19, 50, 00)),
+      );
+    });
+    test('(MINUTELY)', () {
+      final rule = RecurrenceRule.fromString('RRULE:FREQ=MINUTELY;INTERVAL=1');
+      final start = DateTime.utc(2026, 01, 05, 18, 50, 01);
+      final after = DateTime.utc(2026, 01, 05, 20, 24, 54, 548, 180);
+      expect(
+        rule.getInstances(start: start, after: after).first,
+        equals(DateTime.utc(2026, 01, 05, 20, 25, 01)),
+      );
+    });
+    test('(SECONDLY)', () {
+      final rule = RecurrenceRule.fromString('RRULE:FREQ=SECONDLY;INTERVAL=1');
+      final start = DateTime.utc(2026, 01, 05, 18, 50, 00, 12, 34);
+      final after = DateTime.utc(2026, 01, 06, 21, 24, 54, 548, 180);
+      expect(
+        rule.getInstances(start: start, after: after).first,
+        equals(DateTime.utc(2026, 01, 06, 21, 24, 55, 12, 34)),
+      );
+    });
   });
 }

test/rrule_ical_test.dart

@@ -851,4 +851,25 @@ void main() {
       DateTime.utc(2007, 3, 30, 9, 0, 0),
     ],
   );
+  testRrule(
+    '#82: Calculation of frequency SECONDLY is not increasing seconds correctly',
+    string: 'RRULE:FREQ=SECONDLY;INTERVAL=21',
+    rrule: RecurrenceRule(
+      frequency: Frequency.secondly,
+      interval: 21,
+    ),
+    start: DateTime.utc(1997, 9, 2, 9, 0, 3),
+    expected: [
+      DateTime.utc(1997, 9, 2, 9, 0, 03),
+      DateTime.utc(1997, 9, 2, 9, 0, 24),
+      DateTime.utc(1997, 9, 2, 9, 0, 45),
+      DateTime.utc(1997, 9, 2, 9, 1, 06),
+      DateTime.utc(1997, 9, 2, 9, 1, 27),
+      DateTime.utc(1997, 9, 2, 9, 1, 48),
+      DateTime.utc(1997, 9, 2, 9, 2, 09),
+      DateTime.utc(1997, 9, 2, 9, 2, 30),
+      DateTime.utc(1997, 9, 2, 9, 2, 51),
+    ],
+    isInfinite: true,
+  );
 }