PayPal payment processing delay of several hours

Hey Guys,

A few days ago I've implemented PayPals' Instant Payment Notification service to automate the membership upgrade process related to my website. When I tested the IPN process I used sandbox, and I changed the following values in the HTML form code to go live:

<form method="post" name="paypalsubmit" action="[B]https://www.paypal.com/cgi-bin/webscr[/B]">
<input type="hidden" name="rm" value="2"/><input type="hidden" name="cmd" value="_xclick"/>
<input type="hidden" name="business" value="[B]info@mywebsite.com[/B]"/>
<input type="hidden" name="return" value="http://www.mywebsite.com/?page=accupgrade_complete"/>
<input type="hidden" name="cancel_return" value="http://www.mywebsite.com/?page=accupgrade_cancel"/>
<input type="hidden" name="notify_url" value="http://www.mywebsite.com/?page=accupgrade_verify"/>
<input type="hidden" name="no_shipping" value="1"><input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="item_name" value="1 year premium membership"/><input type="hidden" name="amount" value="47.88"/>
<input type="hidden" name="on0" value="Your account"/><input type="hidden" name="os0" value="membername"/>
</form>

Code (markup):

The two bold values were https://www.sandbox.paypal.com/cgi-bin/webscr and .

While testing with the sandbox version I coud not find any problems and the account was upgraded straightaway. But after going live, it takes about 6 hours before my server upgrades the account and I receive a notification from my own server (not the paypal email).

My problem consists of two questions:
- Are the two bold (see code above) changes I made enough to go live, or have I forgotten someting?
- Is it normal for PayPal to process the IPN after 6 hours? It doesn't really sound like an Instant Payment Notification, does it?

Thanks for the help!