I don't use Harlowe, but hypothetically you could modify the few bits of SugarCube code to Harlowe code in my answer to this question "Using JQuery for credits" and that should do the trick.
Hope that helps! :-)
{(set: $credit1 to '')(set: $credit2 to '')(set: $credit3 to '')(set: $credit4 to '')(set: $credit5 to '')}(live: 0.1s)[$credit1 $credit2 $credit3 $credit4 $credit5] (live: 2s:)[(set: $credit5 to 'Director and Writer: Christopher Nolan')(stop:)] (live: 3s)[(set: $credit4 to 'Director and Writer: Christopher Nolan')(set: $credit5 to 'Producer: Emma Thomas')(stop:)] (live: 4s)[(set: $credit3 to 'Director and Writer: Christopher Nolan')(set: $credit4 to 'Producer: Emma Thomas')(set: $credit5 to 'Producer: Christopher Nolan')(stop:)] (live: 5s)[(set: $credit2 to 'Director and Writer: Christopher Nolan')(set: $credit3 to 'Producer: Emma Thomas')(set: $credit4 to 'Producer Christopher Nolan')(set: $credit5 to 'Executive Producer: Chris Brigham')(stop:)] (live: 6s)[(set: $credit1 to 'Director and Writer: Christopher Nolan')(set: $credit2 to 'Producer: Emma Thomas')(set: $credit3 to 'Producer Christopher Nolan')(set: $credit4 to 'Executive Producer: Chris Brigham')(set: $credit5 to 'Executive Producer: Thomas Tull')(stop:)]
Try this.