diff --git a/docs/api/apiv3/components/schemas/user_non_working_time_collection_model.yml b/docs/api/apiv3/components/schemas/user_non_working_time_collection_model.yml
index 1d302ca1340..a45cf41b9c0 100644
--- a/docs/api/apiv3/components/schemas/user_non_working_time_collection_model.yml
+++ b/docs/api/apiv3/components/schemas/user_non_working_time_collection_model.yml
@@ -41,19 +41,21 @@ example:
     elements:
       - _type: UserNonWorkingTime
         id: 7
-        date: "2025-06-18"
+        startDate: "2025-06-16"
+        endDate: "2025-06-20"
         _links:
           self:
-            href: /api/v3/users/42/non_working_times/2025-06-16
+            href: /api/v3/users/42/non_working_times/7
           user:
             href: /api/v3/users/42
             title: Jane Doe
       - _type: UserNonWorkingTime
         id: 8
-        date: "2025-12-24"
+        startDate: "2025-12-24"
+        endDate: "2025-12-24"
         _links:
           self:
-            href: /api/v3/users/42/non_working_times/2025-12-24
+            href: /api/v3/users/42/non_working_times/8
           user:
             href: /api/v3/users/42
             title: Jane Doe
diff --git a/spec/models/user_working_hours_spec.rb b/spec/models/user_working_hours_spec.rb
index f883e7e50b8..027575d7b7e 100644
--- a/spec/models/user_working_hours_spec.rb
+++ b/spec/models/user_working_hours_spec.rb
@@ -38,13 +38,32 @@ RSpec.describe UserWorkingHours do
 
     it { is_expected.to validate_presence_of(:valid_from) }
 
+    # The *_hours virtual attributes have a converting setter (hours → minutes), so
+    # shoulda-matchers cannot induce invalid states through it. We bypass the setter
+    # and write directly to the underlying minute column instead.
     %i[monday tuesday wednesday thursday friday saturday sunday].each do |day|
-      it { is_expected.to validate_presence_of(:"#{day}_hours") }
+      describe "##{day}_hours" do
+        it "is invalid when exceeding 24 hours" do
+          subject.public_send(:"#{day}=", (24.5 * 60).round)
+          expect(subject).not_to be_valid
+          expect(subject.errors[:"#{day}_hours"]).to be_present
+        end
 
-      it do
-        expect(subject).to validate_numericality_of(:"#{day}_hours")
-                                                    .is_greater_than_or_equal_to(0)
-                                                    .is_less_than_or_equal_to(24)
+        it "is invalid when negative" do
+          subject.public_send(:"#{day}=", -60)
+          expect(subject).not_to be_valid
+          expect(subject.errors[:"#{day}_hours"]).to be_present
+        end
+
+        it "is valid at 0 hours" do
+          subject.public_send(:"#{day}=", 0)
+          expect(subject).to be_valid
+        end
+
+        it "is valid at 24 hours" do
+          subject.public_send(:"#{day}=", 24 * 60)
+          expect(subject).to be_valid
+        end
       end
     end
 
diff --git a/spec/support/pages/users/non_working_times.rb b/spec/support/pages/users/non_working_times.rb
index 29fa5bf748a..f5ae2814fe7 100644
--- a/spec/support/pages/users/non_working_times.rb
+++ b/spec/support/pages/users/non_working_times.rb
@@ -135,7 +135,7 @@ module Pages
       end
 
       def expect_working_days_count(count)
-        expect(page).to have_field(I18n.t(:label_working_days), disabled: true, with: count.to_s)
+        expect(page).to have_field(I18n.t(:label_working_days), with: count.to_s)
       end
 
       def expect_sidebar_entry(text)