You will need to set it in code. Open up the script.js file for your solution and search for the data connection (aka connector). If you cannot find it you may need to add code in your OnLoad event handler to modify the timeout. In addition, you will have to uncheck "Automatically load data on load" and programmatically call the data connection after setting the timeout.
Patrick Halstead [InfoPath MVP]
InfoPathDev
Patrick Halstead
Project Manager at Qdabra