What would be the most accurate way to calculate time in this case?

See more:

C#

DateTime

TimeSpan

Hi!
I'm working on a time tracking system which I want to use in a MVC 5 app.
Here is what I have so far:

My (simplified) class ClockInOut.cs

public Guid Id { get; set; }
public DateTime ClockIn { get; set; }
public DateTime ClockOut { get; set; }
public TimeSpan Duration { get; set; }

Now in my view the user has two buttons. Clock in and clock out.

These are the controller actions:

public ActionResult ClockIn()
{
    var model = new ZeitBuchungDto()
                {
                    Id = Guid.NewGuid(),
                    Kommen = DateTime.Now,
                    Gehen = new DateTime(9998,12,31,0,0,0),
                };
    
    var convertToEntity = Mapper.Map<ZeitBuchungDto, ZeitBuchung>(model);
    
    zeitContext.ZeitBuchung.Add(convertToEntity);
    zeitContext.SaveChanges();

    return Json(new { success = true }, JsonRequestBehavior.AllowGet);
}

public ActionResult ClockOut()
{
    using (var db = new ZeitContext())
          {
              db.ZeitBuchung.Attach(convertToEntity);
              convertToEntity.Gehen = DateTime.Now;
              convertToEntity.AktuellGebucht = false;
              convertToEntity.Gesamtdauer = convertToEntity.Gehen - zeitKommen;
              db.Entry(convertToEntity).Property(x => x.Gesamtdauer).IsModified = true;
              db.Entry(convertToEntity).Property(x => x.Gehen).IsModified = true;
              db.SaveChanges();
           }
    return Json(new { success = true }, JsonRequestBehavior.AllowGet);
}

Now what's coming next is the point with which I'm not satisfied:

private IEnumerable<TimeSpan> GetTotalTime()
{
    var totalTime = myContext.MyEntity.Select(m => m.Duration).AsEnumerable();

    return totalTime;
}

public ActionResult Index()
{
    IEnumerable<TimeSpan> time = GetTotalTime();
    var totalTime = time.Sum(s => s.Ticks);
    var convertedTime = TimeSpan.FromTicks(totalTime).ToString(@"hh\:mm");

    ViewBag.Hours = convertedTime;

    return View(model);
}

What I have tried:

Actually all this stuff works but I have a feeling this conversion is pretty inaccurate.

Throughout my tests I noticed that sometimes the numbers I see don't add up. Might be just a rounding issue but I'm still pretty new to programming so I can't really judge on that.

What I would like to have is an accurate view. Take a look at this pic:
http://fs5.directupload.net/images/170905/zhvrlb4j.png
Where I put the circle, I assume this just got rounded up to 1 minute - which isn't too bad right now. But imagine you have a whole month of data and it just rounds up to a good amount of minutes - the person checking the times at the end of the month might get confused.

So my reason for asking - have mercy with my code, it's probably not really good lol - but anyway, how would I get an accurate illustration of the various times.

Hope you have some suggestions....

Thanks in advance :)

Paul