Flip direction to avoid breaking other usages

osu.Game/Rulesets/Objects/Types/IHasDuration.cs

@@ -8,17 +8,27 @@ namespace osu.Game.Rulesets.Objects.Types
     /// <summary>
     /// A HitObject that ends at a different time than its start time.
     /// </summary>
-    public interface IHasDuration
+#pragma warning disable 618
+    public interface IHasDuration : IHasEndTime
+#pragma warning restore 618
     {
+        double IHasEndTime.EndTime
+        {
+            get => EndTime;
+            set => Duration = (Duration - EndTime) + value;
+        }
+
+        double IHasEndTime.Duration => Duration;
+
         /// <summary>
         /// The time at which the HitObject ends.
         /// </summary>
-        double EndTime { get; }
+        new double EndTime { get; }
 
         /// <summary>
         /// The duration of the HitObject.
         /// </summary>
         [JsonIgnore]
-        double Duration { get; set; }
+        new double Duration { get; set; }
     }
 }

osu.Game/Rulesets/Objects/Types/IHasEndTime.cs

@@ -2,11 +2,25 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using Newtonsoft.Json;
 
 namespace osu.Game.Rulesets.Objects.Types
 {
+    /// <summary>
+    /// A HitObject that ends at a different time than its start time.
+    /// </summary>
     [Obsolete("Use IHasDuration instead.")] // can be removed 20201126
-    public interface IHasEndTime : IHasDuration
+    public interface IHasEndTime
     {
+        /// <summary>
+        /// The time at which the HitObject ends.
+        /// </summary>
+        [JsonIgnore]
+        double EndTime { get; set; }
+
+        /// <summary>
+        /// The duration of the HitObject.
+        /// </summary>
+        double Duration { get; }
     }
 }