diff --git a/src/core/singletons/tests/time.test.ts b/src/core/singletons/tests/time.test.ts
new file mode 100644
index 000000000..b5f2122f8
--- /dev/null
+++ b/src/core/singletons/tests/time.test.ts
@@ -0,0 +1,69 @@
+// (C) Copyright 2015 Moodle Pty Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import { mockTranslate } from '@/testing/utils';
+import { CoreTime } from '@singletons/time';
+
+describe('CoreTime singleton', () => {
+
+    it('formats time in a human readable format', () => {
+        mockTranslate({
+            'core.days': 'days',
+            'core.day': 'day',
+            'core.hours': 'hours',
+            'core.hour': 'hour',
+            'core.mins': 'mins',
+            'core.min': 'min',
+            'core.now': 'now',
+            'core.secs': 'secs',
+            'core.sec': 'sec',
+            'core.years': 'years',
+            'core.year': 'year',
+        });
+
+        expect(CoreTime.formatTime(0)).toEqual('now');
+        expect(CoreTime.formatTime(-5)).toEqual('5 secs');
+        expect(CoreTime.formatTime(61)).toEqual('1 min 1 sec');
+        expect(CoreTime.formatTime(7321)).toEqual('2 hours 2 mins');
+        expect(CoreTime.formatTime(352861)).toEqual('4 days 2 hours');
+        expect(CoreTime.formatTime(31888861)).toEqual('1 year 4 days');
+        expect(CoreTime.formatTime(-31888861)).toEqual('1 year 4 days');
+
+        // Test different precisions.
+        expect(CoreTime.formatTime(31888861, 1)).toEqual('1 year');
+        expect(CoreTime.formatTime(31888861, 3)).toEqual('1 year 4 days 2 hours');
+        expect(CoreTime.formatTime(31888861, 4)).toEqual('1 year 4 days 2 hours 1 min');
+        expect(CoreTime.formatTime(31888861, 5)).toEqual('1 year 4 days 2 hours 1 min 1 sec');
+    });
+
+    it('formats time in a "short" human readable format', () => {
+        expect(CoreTime.formatTimeShort(0)).toEqual('0\'\'');
+        expect(CoreTime.formatTimeShort(61)).toEqual('1\' 1\'\'');
+        expect(CoreTime.formatTimeShort(7321)).toEqual('122\' 1\'\'');
+    });
+
+    it('calls a function only once', () => {
+        const testFunction = jest.fn();
+        const onceFunction = CoreTime.once(testFunction);
+
+        expect(testFunction).not.toHaveBeenCalled();
+
+        onceFunction('foo', 'bar');
+        expect(testFunction).toHaveBeenCalledWith('foo', 'bar');
+
+        onceFunction('baz');
+        expect(testFunction).toHaveBeenCalledTimes(1);
+    });
+
+});
diff --git a/src/core/singletons/time.ts b/src/core/singletons/time.ts
index 5c95ed837..fd855b383 100644
--- a/src/core/singletons/time.ts
+++ b/src/core/singletons/time.ts
@@ -39,7 +39,7 @@ export class CoreTime {
         let remainder = totalSecs - (years * CoreConstants.SECONDS_YEAR);
         const days = Math.floor(remainder / CoreConstants.SECONDS_DAY);
 
-        remainder = totalSecs - (days * CoreConstants.SECONDS_DAY);
+        remainder = remainder - (days * CoreConstants.SECONDS_DAY);
 
         const hours = Math.floor(remainder / CoreConstants.SECONDS_HOUR);
         remainder = remainder - (hours * CoreConstants.SECONDS_HOUR);
diff --git a/src/testing/utils.ts b/src/testing/utils.ts
index 4f097a35a..4b9091735 100644
--- a/src/testing/utils.ts
+++ b/src/testing/utils.ts
@@ -19,7 +19,7 @@ import { Observable, Subject } from 'rxjs';
 import { sep } from 'path';
 
 import { CORE_SITE_SCHEMAS } from '@services/sites';
-import { CoreSingletonProxy, Network, Platform } from '@singletons';
+import { CoreSingletonProxy, Network, Platform, Translate } from '@singletons';
 import { CoreTextUtilsProvider } from '@services/utils/text';
 
 import { TranslatePipeStub } from './stubs/pipes/translate';
@@ -269,3 +269,14 @@ export function wait(time: number): Promise<void> {
         }, time);
     });
 }
+
+/**
+ * Mocks translate service with certain translations.
+ *
+ * @param translations List of translations.
+ */
+export function mockTranslate(translations: Record<string, string>): void {
+    mockSingleton(Translate, {
+        instant: (key) => translations[key] ?? key,
+    });
+}