AJAX :: Alert In UpdatePanel After Page Has Fully Loaded?

Have a GridView in an UpdatePanel, all works fine. Click the Submit() button which updates the database on postback, then the GridView is bound in code and I register an alert:

ScriptManager.RegisterStartupScript(this.UpdatePanel1, typeof(string), "dopopup", "alert('Operation successful!');", true);

Calling UpdatePanel1.Update() causes the popup to appear. All fine but what I am noticing is that the alert occurs just before the page has fully updated and is causing a few minor layout issues that are resolved when the alert button is closed (by clicking OK). Is there a way to generate an alert after a full UpdatePanel refresh, so something like:

ScriptManager.RegisterFullyLoadedScript(this.UpdatePanel1, typeof(string), "dopopup", "alert('Operation successful!');", true);

I tried a simple wait() in the code like this:

ScriptManager.RegisterStartupScript(this.UpdatePanel1, typeof(string), "dopopup", "wait(100);alert('Operation successful!');", true);

But this didn't work.