transaction timeout configuration

Hi Team,

We are using SOAP UI to test our https REST webservice and we have set the timeout limit to 20 seconds at interface level. In the SOAP UI we have set the following configuration under preference>HTTP Settings, however we are getting gateway timeout 504 error, if the response time exceeds 10 seconds. 

Socket Timeout(ms):20000

Please suggest a way to increase the timeout limit to 20 seconds. Thanks in advance.

Regards,

Sudipta