Add a max duration while still allowing user to press space to continue

I want to set a maximum time limit on an essay question. The instructions for the [I]d[/I] parameter say that it sets a duration [I]instead[/I] of letting the user press space to continue.

If people finish the essay early, I don't want them to have to wait the full duration. How do I let them advance with space bar while still setting a time limit?

Thanks.

There is no real function for this aside from telling them that they can hit "Esc" (escape) to exit if they happen to be done early. The first sample in the samples folder illustrates this with a timed essay if you want to check it out. Please let me know if that doesn't address your question.