✅ Reading Time Stamps From Database and Summing Time c#

// database file
public List<ShiftModel> GetShiftEntries()
{
    using SQLiteConnection conn = new(_dbFilePath);
    using SQLiteCommand cmd = conn.CreateCommand();
    SQLiteDataReader reader;

    cmd.CommandText = @"SELECT * FROM records";
    reader = cmd.ExecuteReader();

    List<ShiftModel> shiftEntries = new();

    while (reader.Read())
    {
        shiftEntries.Add(new ShiftModel()
        {
            StartTime = reader["StartTime"].ToString(),
            EndTime = reader["EndTime"].ToString(),
            StartMileage = Convert.ToInt32(reader["StartMileage"].ToString()),
            EndMileage = Convert.ToInt32(reader["EndMileage"].ToString())
        });
    }

    return shiftEntries;
}

public TotalModel GetTotals()
{
    List<ShiftModel> shifts = GetShiftEntries();

    Helpers hp = new();
    hp.SumTime(shifts);
}

// helpers file
internal TimeSpan SumTime(List<ShiftModel> list)
{
}

// database file
public List<ShiftModel> GetShiftEntries()
{
    using SQLiteConnection conn = new(_dbFilePath);
    using SQLiteCommand cmd = conn.CreateCommand();
    SQLiteDataReader reader;

    cmd.CommandText = @"SELECT * FROM records";
    reader = cmd.ExecuteReader();

    List<ShiftModel> shiftEntries = new();

    while (reader.Read())
    {
        shiftEntries.Add(new ShiftModel()
        {
            StartTime = reader["StartTime"].ToString(),
            EndTime = reader["EndTime"].ToString(),
            StartMileage = Convert.ToInt32(reader["StartMileage"].ToString()),
            EndMileage = Convert.ToInt32(reader["EndMileage"].ToString())
        });
    }

    return shiftEntries;
}

public TotalModel GetTotals()
{
    List<ShiftModel> shifts = GetShiftEntries();

    Helpers hp = new();
    hp.SumTime(shifts);
}

// helpers file
internal TimeSpan SumTime(List<ShiftModel> list)
{
}