Does a variable take up a significant amount of space?  If so, can one be unloaded somehow once it is no longer necessary?

private void tmrCheck_Tick(object sender, EventArgs e)
        {
            // This opens the database.
            string conString = "Provider=Microsoft.Jet.OLEDB.4.0;"
            + "Data Source=\\\\DPR\\micromain_database\\msData_2.mdb";
            OleDbConnection msData_2Connection = new OleDbConnection(conString);
 
            // This creates the SELECT statement.
            string selectStatement = "SELECT MAX(Created) AS MaxOfCreated FROM tblWO";
 
            OleDbCommand objCmdSelect = new OleDbCommand(selectStatement, msData_2Connection);
            OleDbDataAdapter objAdapter1 = new OleDbDataAdapter();
            objAdapter1.SelectCommand = objCmdSelect;
            DataSet objDataset1 = new DataSet();
            objAdapter1.Fill(objDataset1);
 
            // This turns the result of the query into a string.
            string strResult = objDataset1.Tables[0].Rows[objDataset1.Tables[0].Rows.Count - 1]["MaxOfCreated"].ToString();
 
            // This turns the result of the query into a DateTime.
            DateTime dtResult = DateTime.Parse(strResult);
 
            // This sets a variable with the current time.
            DateTime dtToday = DateTime.Now;
 
            // This sets a variable for five minutes ago by subtracting 5 from dtToday.
            DateTime dtFiveMinutesAgo;
            dtFiveMinutesAgo = dtToday.AddMinutes(-5);
 
            // This compares dtResult to dtFiveMinutesAgo.
            if (dtResult > dtFiveMinutesAgo)
            {
                MessageBox.Show(this, "New work orders created!", "MicroMain Alert!", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
 
            // This prints the result in the textbox.
            textBox1.Text = strResult;
 
            // This prints the time of the check in the other textbox.
            DateTime dtNow = DateTime.Now;
            string strNow = dtNow.ToString();
            textBox2.Text = strNow;
 
            // This creates the SELECT statement for the asset.
            string selectStatement2 = "SELECT MAX(Asset) AS LastAsset FROM tblWO GROUP BY Created";
 
            OleDbCommand objCmdSelect2 = new OleDbCommand(selectStatement2, msData_2Connection);
            OleDbDataAdapter objAdapter2 = new OleDbDataAdapter();
            objAdapter2.SelectCommand = objCmdSelect2;
            DataSet objDataset2 = new DataSet();
            objAdapter2.Fill(objDataset2);
 
            // This turns the other query result into a string.
            string strResultAsset = objDataset2.Tables[0].Rows[objDataset2.Tables[0].Rows.Count - 1]["LastAsset"].ToString();
 
            //This prints that result in a textbox.
            textBox3.Text = strResultAsset;
 
            // Close the connection.
            msData_2Connection.Close();
 
        }