using System;
using System.Collections.Generic;
using System.Linq;


class Program
    {
        static void Main(string[] args)
        {
           
        var records = new List<Record>
            {
                new Record { Id = 1, StartDate = new DateTime(2013, 1, 1, 10, 20, 0), EndDate = new DateTime(2013, 1, 1, 10, 25, 0)},
                new Record { Id = 1, StartDate = new DateTime(2013, 1, 1, 10, 40, 0), EndDate = new DateTime(2013, 1, 1, 11, 15, 0)},
                new Record { Id = 2, StartDate = new DateTime(2013, 1, 2, 10, 20, 0), EndDate = new DateTime(2013, 1, 2, 10, 25, 0)},
                new Record { Id = 1, StartDate = new DateTime(2013, 1, 2, 11, 20, 0), EndDate = new DateTime(2013, 1, 2, 12, 22, 0)},
            };


        var query = from r in records
                    group r by new { r.Id, r.StartDate.Date } into g
                    select new
                    {
                        g.Key.Id,
                        g.Key.Date,
                        TotalDuration = g.Sum(x => (x.EndDate - x.StartDate).TotalMinutes)
                    };                    
                    
            foreach(var item in query)
                Console.WriteLine("{0} {1} {2} min", item.Id, item.Date.ToShortDateString(), item.TotalDuration);
        }
    }

    public class Record
    {
        public int Id { get; set; }
        public DateTime StartDate { get; set; }
        public DateTime EndDate { get; set; }
        public int Chapter { get; set; }
    }