PlistDateIssueDemo.cs

using System;
using System.Runtime.InteropServices;

namespace PlistDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            const string xml = @"<?xml version=""1.0"" encoding=""UTF-8""?>
<!DOCTYPE plist PUBLIC ""-//Apple//DTD PLIST 1.0//EN"" ""http://www.apple.com/DTDs/PropertyList-1.0.dtd"">
<plist version=""1.0"">
<dict>
    <key>Last Backup Date</key>
    <date>2016-04-06T10:16:17Z</date>
</dict>
</plist>
";
            IntPtr dictPtr;
            Plist.plist_from_xml(xml, (uint) xml.Length, out dictPtr);

            var backupDatePtr = Plist.plist_dict_get_item(dictPtr, "Last Backup Date");
            int sec, usec;
            Plist.plist_get_date_val(backupDatePtr, out sec, out usec);

            var date = new DateTime(2001, 1, 1, 0, 0, 0, DateTimeKind.Utc).AddSeconds(sec);

            
            Console.WriteLine($"Parsing XML:\n{xml}\n\n=======================");

            Console.WriteLine($"{date} ({date.Kind}) from secs: {sec}");
        }
    }

    internal static class Plist
    {
        private const string DllName = @"C:\Programs\imobiledevice\libplist.dll";

        [DllImport(DllName, EntryPoint = "plist_from_xml", CallingConvention = CallingConvention.Cdecl)]
        public static extern void plist_from_xml([MarshalAs(UnmanagedType.LPStr)]string xml, uint length, out IntPtr nodePtr);

        [DllImport(DllName, EntryPoint = "plist_dict_get_item", CallingConvention = CallingConvention.Cdecl)]
        public static extern IntPtr plist_dict_get_item(IntPtr node, [In, MarshalAs(UnmanagedType.LPStr)] string key);

        [DllImport(DllName, EntryPoint = "plist_get_date_val", CallingConvention = CallingConvention.Cdecl)]
        public static extern void plist_get_date_val(IntPtr node, out int sec, out int usec);
    }
}

The output of the program is:

Parsing XML:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Last Backup Date</key>
    <date>2016-04-06T10:16:17Z</date>
</dict>
</plist>


=======================
06.04.2016 11:16:17 (Utc) from secs: 481634177