Index: src/natools-cron.adb
==================================================================
--- src/natools-cron.adb
+++ src/natools-cron.adb
@@ -79,10 +79,21 @@
       return Result : Cron_Entry do
          Result.Set (Time, Callback);
       end return;
    end Create;
 
+
+   function Create
+     (Origin : in Ada.Calendar.Time;
+      Callback : in Cron.Callback'Class)
+     return Cron_Entry is
+   begin
+      return Result : Cron_Entry do
+         Result.Set (Origin, Callback);
+      end return;
+   end Create;
+
 
    function Create
      (Period : in Duration;
       Callback : in Cron.Callback'Class)
      return Cron_Entry is
@@ -108,10 +119,19 @@
       Self.Reset;
       Self.Callback.Replace (Create'Access);
       Database.Insert (Time, Self.Callback);
    end Set;
 
+
+   procedure Set
+     (Self : in out Cron_Entry;
+      Origin : in Ada.Calendar.Time;
+      Callback : in Cron.Callback'Class) is
+   begin
+      Set (Self, (Origin, 0.0), Callback);
+   end Set;
+
 
    procedure Set
      (Self : in out Cron_Entry;
       Period : in Duration;
       Callback : in Cron.Callback'Class) is

Index: src/natools-cron.ads
==================================================================
--- src/natools-cron.ads
+++ src/natools-cron.ads
@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
--- Copyright (c) 2014, Natacha Porté                                        --
+-- Copyright (c) 2014-2015, Natacha Porté                                   --
 --                                                                          --
 -- Permission to use, copy, modify, and distribute this software for any    --
 -- purpose with or without fee is hereby granted, provided that the above   --
 -- copyright notice and this permission notice appear in all copies.        --
 --                                                                          --
@@ -52,10 +52,16 @@
      (Time : in Periodic_Time;
       Callback : in Cron.Callback'Class)
      return Cron_Entry;
       --  Create a new entry with the given parameters
 
+   function Create
+     (Origin : in Ada.Calendar.Time;
+      Callback : in Cron.Callback'Class)
+     return Cron_Entry;
+      --  Create a new entry that executes only once, at the given time
+
    function Create
      (Period : in Duration;
       Callback : in Cron.Callback'Class)
      return Cron_Entry;
       --  Create a new entry starting within a period from now
@@ -64,10 +70,16 @@
      (Self : in out Cron_Entry;
       Time : in Periodic_Time;
       Callback : in Cron.Callback'Class);
       --  Reset an entry with the given parameters
 
+   procedure Set
+     (Self : in out Cron_Entry;
+      Origin : in Ada.Calendar.Time;
+      Callback : in Cron.Callback'Class);
+      --  Reset entry with the given parameters, running only once
+
    procedure Set
      (Self : in out Cron_Entry;
       Period : in Duration;
       Callback : in Cron.Callback'Class);
       --  Reset entry with the given parameters, starting one period from now