diff --git a/src/SharpCompress/Common/Arc/ArcEntryHeader.cs b/src/SharpCompress/Common/Arc/ArcEntryHeader.cs
index 824d90eb..7be8d8ec 100644
--- a/src/SharpCompress/Common/Arc/ArcEntryHeader.cs
+++ b/src/SharpCompress/Common/Arc/ArcEntryHeader.cs
@@ -69,16 +69,8 @@ namespace SharpCompress.Common.Arc
 
         public static DateTime ConvertToDateTime(long rawDateTime)
         {
-            // Extract components using bit manipulation
-            int year = (int)((rawDateTime >> 25) & 0x7F) + 1980;
-            int month = (int)((rawDateTime >> 21) & 0xF);
-            int day = (int)((rawDateTime >> 16) & 0x1F);
-            int hour = (int)((rawDateTime >> 11) & 0x1F);
-            int minute = (int)((rawDateTime >> 5) & 0x3F);
-            int second = (int)((rawDateTime & 0x1F) * 2); // Multiply by 2 since DOS seconds are stored as halves
-
-            // Return as a DateTime object
-            return new DateTime(year, month, day, hour, minute, second);
+            // Convert Unix timestamp to DateTime (UTC)
+            return DateTimeOffset.FromUnixTimeSeconds(rawDateTime).UtcDateTime;
         }
     }
 }
diff --git a/src/SharpCompress/IO/ReadOnlySubStream.cs b/src/SharpCompress/IO/ReadOnlySubStream.cs
index cd39335e..632d350f 100644
--- a/src/SharpCompress/IO/ReadOnlySubStream.cs
+++ b/src/SharpCompress/IO/ReadOnlySubStream.cs
@@ -13,7 +13,7 @@ internal class ReadOnlySubStream : NonDisposingStream
     public ReadOnlySubStream(Stream stream, long? origin, long bytesToRead)
         : base(stream, throwOnDispose: false)
     {
-        if (origin != null)
+        if (origin != null && stream.Position != origin.Value)
         {
             stream.Position = origin.Value;
         }
@@ -31,7 +31,7 @@ internal class ReadOnlySubStream : NonDisposingStream
 
     public override void Flush() { }
 
-    public override long Length => throw new NotSupportedException();
+    public override long Length => base.Length;
 
     public override long Position
     {