String Date = "17/3/2015";
DateTime StartDate = Convert.ToDateTime(Date);
DateTime EndDate = DateTime.Now.AddDays(1);
var users = from A in Sessions
where (A.StartDate >= StartDate && A.StartDate < EndDate)
select new {A.SessionKey,A.StartDate,A.EndDate,A.UserId};
List<ConnectedUser> report = new List<ConnectedUser>();
report.Add(new ConnectedUser(StartDate,users.ToList().GroupBy(u=>u.UserId).ToList().Count()));
Console.WriteLine(report);

}

public class ConnectedUser
{
public DateTime Date;
public int UsersConnected;
public ConnectedUser(DateTime Date,int UsersConnected)
	{
	this.Date = Date;
	this.UsersConnected = UsersConnected;
	}