HTML can only record data that has been submitted. Setting the custom item to display for five minutes means after five minutes, the program will move on, and any data that has not been submitted will be lost.

Are you familiar with javascript? Because with javascript, which can be included in HTML custom items, you can command that after a set period of time (e.g., 5 min), the form is submitted.

This can be accomplished with the javascript command [settimeout()].

If you're not familiar with javascript, here are some resources.

http://www.w3schools.com/js/js_intro.asp
http://www.w3schools.com/js/js_timing.asp

Hope this helps.