What is the test for denying a post-conviction habeas relief petition?

The district court denied appellant's petition on the ground that appellant had waited an unreasonable period of time before bringing the petition. We concluded in Groesbeck v. Warden, 100 Nev. 259, 679 P.2d 1268 (1984), that it was proper to deny a petition for post-conviction habeas relief brought after an unreasonably long delay because of the inherent difficulties occasioned by such a petition.