Datetimepicker Selection just for one day...?

Question

Datetimepicker from and datetimepicker to....

Work just for one day exp, 16.03.2018....16.03.2018

Work fine

If choose 01.03.2018 to 16.03.2018 dont work...

What I wrong?

 

private void radni_sati2()
{
    String cs = "Data Source=.\\SQLEXPRESS;Initial Catalog=bss_prijava_radnika;Integrated Security=True";
    using (SqlConnection openCon = new SqlConnection(cs))
    {         string saveStaff = "SELECT a.IdPrijava, a.redni_broj , a.radnik, isnull(convert(varchar(20), a.vrijemeodjave, 113), '') as vrijemeodjave, convert(varchar(20), b.vrijemeprijave, 113) as vrijemeprijave, "
            + "CASE WHEN (DATEDIFF(SECOND, b.vrijemeprijave, a.vrijemeodjave) / 3600) > 8 THEN 8 ELSE(DATEDIFF(SECOND, b.vrijemeprijave, a.vrijemeodjave) / 3600) END  AS radni_sati, "
            + "CASE WHEN(DATEDIFF(SECOND, b.vrijemeprijave, a.vrijemeodjave) / 3600) > 8  THEN(DATEDIFF(SECOND, b.vrijemeprijave, a.vrijemeodjave) / 3600) - 8  ELSE NULL END  AS prekovremeni "
            + "FROM(SELECT IdPrijava, redni_broj, radnik, vrijemeodjave, ROW_Number() OVER(Partition By IdPrijava ORDER BY vrijemeprijave) as RowNum "
            + "FROM dbo.prijava_radnika) a INNER JOIN(SELECT IdPrijava, redni_broj, radnik, vrijemeprijave, (ROW_Number() OVER(Partition By IdPrijava ORDER BY vrijemeprijave) - 1) as RowNumMinusOne FROM dbo.prijava_radnika) b ON a.IdPrijava = b.IdPrijava where 1 = 1 ";
        if (!string.IsNullOrEmpty(textBox1.Text))
        {
            saveStaff += " AND a.radnik LIKE \'%" + textBox1.Text + "%\' ";
        }
        if (checkBox1.Checked)
        {
            String strFilterDTP1 = dateTimePicker1.Value.ToString("yyyy-MM-dd");
            String strFilterDTP2 = dateTimePicker2.Value.ToString("yyyy-MM-dd");
            saveStaff += " AND b.vrijemeprijave between '" + strFilterDTP1 + " 00:00:00' AND '" + strFilterDTP1 + " 23:59:59' ";
            saveStaff += " AND a.vrijemeodjave between '" + strFilterDTP2 + " 00:00:00' AND '" + strFilterDTP2 + " 23:59:59' ";
        }
        String someDate = "25 Mar 2018 13:13:00";
        DateTime someDT = DateTime.Parse(someDate);
        Console.WriteLine(saveStaff);