Hi colmullet,
Most offers are completed within a few minutes, but there can be delays if the advertiser has trouble automatically validating your personal information. If 24 hours have passed since you completed the offer and you still haven't received your credits please send a support request to TrialPay.
You can do this by hovering your mouse over the GET CREDITS menu at the top left and clicking on the COMPLETE OFFERS option. When that page loads look for the Contact Us link in the top right hand side and click on it. This will display the offers you currently have open. Locate the survey you completed and click the Contact Us link in the actions column. Fill out the requested information and TrialPay will be able look into that for you. They will contact you if they need more information. TrialPay has very good support and most matters are resolved rather quickly.