Windows Service + Timer

Hi!
I'm writing a windows service which should take an XML file from a dir, parse it and put some information on SQL.
This work should be done once in hour. So I decided to use System.Timers. This will be my first time to use System.Timers. So I started to read forums about it's using. I have read many different information and try to use some advices  on my project.
So I got this one:
....
using System.Timers; 
public partial class Service1 : ServiceBase
{
private System.Timers.Timer _timer = null;
public static string location = ConfigurationManager.AppSettings.GetValues("DirPath").First();
public static string xname = ConfigurationManager.AppSettings.GetValues("FilePath").First();
public static string fname = ConfigurationManager.AppSettings.GetValues("FileName").First();
public static string uid = ConfigurationManager.AppSettings.GetValues("Uid").First();
public static int ...