Chronoforms, and some other form components, allows you to insert php code. So you could add php code that inserts the current time into the user's session (the JUser object) when the form is presented to the user, then when the form is processed, check the current time against the time recorded in the JUser object, and accept or reject the form based on time elapsed. This would require a PHP programmer to hack it for you.

If you are looking for a timed quiz component, there is a component available for that: http://extensions.joomla.org/extensions/contacts-and-feedback/quiz-a-surveys/8142