using System;

using System.Linq;

using System.Collections.Generic;

​

namespace Sample

{

    public class TimeSheetLog

    {

       public Guid EmployeeId { get; set; }

       public DateTime ClockInTimeStamp { get; set; }

       public DateTime ClockOutTimeStamp { get; set; }

    }

    public static class ExtensionMethods

    {

        static public double TotalMinutes(this IEnumerable<TimeSheetLog> input, DateTime startPeriod, DateTime endPeriod)

        {

            return TimeSpan.FromTicks

            (

                input

                .Where( a=>

                    a.ClockOutTimeStamp >= startPeriod &&

                    a.ClockInTimeStamp <= endPeriod

                )

                .Select( a=>

                    Math.Min(a.ClockOutTimeStamp.Ticks, endPeriod.Ticks) - 

                    Math.Max(a.ClockInTimeStamp.Ticks, startPeriod.Ticks)

                )

                .Sum()

            )

            .TotalMinutes;

        }

    }

    public class Program

    {

        static public List<TimeSheetLog> testData = new List<TimeSheetLog>

        {

            new TimeSheetLog

            {

                ClockInTimeStamp = DateTime.Parse("1/1/2018 9:00 am"),

                ClockOutTimeStamp = DateTime.Parse("1/1/2018 5:00 pm")

            },

            new TimeSheetLog

            {

                ClockInTimeStamp = DateTime.Parse("1/2/2018 9:00 am"),

                ClockOutTimeStamp = DateTime.Parse("1/2/2018 5:00 pm")

            },

            new TimeSheetLog

            {

                ClockInTimeStamp = DateTime.Parse("1/31/2018 6:00 pm"),

                ClockOutTimeStamp = DateTime.Parse("2/1/2018 9:00 am")

            },

            new TimeSheetLog

            {

                ClockInTimeStamp = DateTime.Parse("2/3/2018 9:00 am"),

                ClockOutTimeStamp = DateTime.Parse("2/3/2018 5:00 pm")

            }

        };

        public static void Main()

        {

            var startPeriod = new DateTime(2018, 1, 1);

            var endPeriod = new DateTime(2018, 1, 31, 23,59,59,999); 

            Console.WriteLine( testData.TotalMinutes(startPeriod, endPeriod).ToString("0.00") );

        }

    }

}