Time Based Triggers in Marketo

We're working on removing gates from our content for people who have already filled out a form. We want to use the trigger "visits webpage" for scoring, but we'd ideally like to trigger it if the person has sat on the page for a set amount of time so that we can assume they've consumed the content and didn't just bounce. We're hoping that by doing this we'll have higher quality MQLs. Is there anyway to do that with Marketo smart campaigns?