When you update domain nameservers it can take up to 72 hours before it is visible to all users of the Internet. The propagation delay is due to Internet providers having to update their records (DNS tables) to reflect the changes.
To check the DNS status of your domain, you can use free DNS lookup websites like this one.
Note: If 72 hours have passed, but you still can't view your website, please don't hesitate to submit a ticket.