Roll TimeWithZones forward in DST-aware manner

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## Upcoming
 
+## 3.2.0 - Nov 3, 2026
+
+- Advance `ActiveSupport::TimeWithZone`s whole days across DST boundaries #339
+
 ## 3.1.0 - Sept 28, 2026
 
 - Fix `business_days_between` not counting extra working dates in full weeks #34 - thanks @anatoliliotych!

lib/business/calendar.rb

@@ -209,7 +209,13 @@ def business_days_between(date1, date2)
     end
 
     def day_interval_for(date)
-      date.is_a?(Date) ? 1 : 3600 * 24
+      if date.is_a?(Date)
+        1
+      elsif defined?(ActiveSupport::TimeWithZone) && date.is_a?(ActiveSupport::TimeWithZone)
+        1.day
+      else
+        3600 * 24
+      end
     end
 
     # Internal method for assigning working days from a calendar config.

lib/business/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Business
-  VERSION = "3.1.0"
+  VERSION = "3.2.0"
 end

spec/business/calendar_spec.rb

@@ -1049,4 +1049,18 @@
 
     it_behaves_like "common"
   end
+
+  context "(using TimeWithZone objects)" do
+    before do
+      stub_const("ActiveSupport::TimeWithZone", Class.new(Time))
+      Integer.define_method(:day) { self * 60 * 60 * 24 }
+    end
+
+    after { Integer.remove_method(:day) }
+
+    let(:date_class) { ActiveSupport::TimeWithZone }
+    let(:day_interval) { 1.day }
+
+    it_behaves_like "common"
+  end
 end