Add option 'at'

lib/periodicity/extensions/active_job.rb

@@ -2,7 +2,7 @@ module Periodicity
   module Extensions
     class ActiveJob
       def self.perform_every(period, *args)
-        @period = period
+        @period = Period.new(period, *args)
       end
     end
   end

lib/periodicity/period.rb

@@ -1,11 +1,24 @@
 module Periodicity
   class Period
-    def initialize(period)
+    def initialize(period, at: nil)
       @period = period
+      @at_hour, @at_min = parse_at(at) if at
     end
 
     def next
-      @period.from_now
+      @period.from_now.change({hour: @at_hour, min: @at_min}.compact)
+    end
+
+    def parse_at(at)
+      case at
+      when String
+        time = Time.parse(at)
+        return time.hour, time.min
+      when Hash
+        return at[:hour], at[:min]
+      else
+        raise "Unknown 'at' format"
+      end
     end
   end
 end