Set due date to later of relative date vs custom date

We are trying to use an Asana form to intake work and kick off projects. Right now, the form takes a “Request Date” as a custom date. We need at least 2 weeks turnaround and want to set the Due Date to the Request Date or 2 weeks after the form is submitted, whichever is later. Is there a way to do this via rules? I can’t seem to find any option to compare these dates.