public class SomeClass
{
    Timer timer;
    public SomeClass()
    {
         timer = new Timer(100);
         timer.Tick += SomeMethod
         timer.Start();
    }
    public void SomeMethod(object sender, EventArgs eventArgs)
    {
         //bla-bla
         //Здесь вызвать!!!
    }
}

public class AnotherClass
{
    SomeClass someField;
    public AnotherClass()
    {
         someField = new SomeClass();
    }

    public int AnotherMethod()
    {
         //bla-bla
         return 1;
    }
}