XML filtering example, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string xml = @"<entry>
						<log_time>20180511-09:06:42</log_time>
						<description>Authentication succeed</description>
						<service>COM</service>
						<sessionid>00000001</sessionid>
						<type>0</type>    <severity>1</severity>
						<user>username</user>
						<host>windows</host>
						<cmd>Login</cmd>
					  </entry>";
		
            // you can use .Load(PATH_TO_FILE) instead
            var doc = XDocument.Parse(xml);

TimeSpan lowerBound = new TimeSpan(8, 0, 0);
            // change this to new TimeSpan(9, 0, 0); and it won't output your sample entry
            TimeSpan upperBound = new TimeSpan(10, 0, 0);

var filteredElements = doc.Elements("entry").Where(entry => IsInRange(entry, lowerBound, upperBound));

foreach(var element in filteredElements)
            {
                Console.WriteLine(element);
            }
        }
        
        public static bool IsInRange(XElement entry, TimeSpan lowerBound, TimeSpan upperBound)
        {
            TimeSpan currentTime = DateTime.ParseExact(entry.Element("log_time").Value, "yyyyMMdd-HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture).TimeOfDay;
            
            if(lowerBound < currentTime && currentTime < upperBound)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,17 sec, absolute running time: 0,19 sec, cpu time: 0,19 sec, average memory usage: 20 Mb, average nr of threads: 4