Конечно, используя таймер. Например:
public void NavigateTo(Uri url) {
webBrowser1.Navigate(url);
timer1.Enabled = true;
}
private void timer1_Tick(object sender, EventArgs e) {
timer1.Enabled = false;
MessageBox.Show("Timeout on navigation");
}
private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) {
if (e.Url == webBrowser1.Url && timer1.Enabled) {
timer1.Enabled = false;
// etc..
}
}