Is a delay in starting deportation proceedings a defense?

The petitioner alleges that he has been denied constitutional rights by a delay in the institution of the deportation proceedings. While this court has held that section 1252(i), calling for the institution of deportation proceedings "as expeditiously as possible after the date of conviction," permits an alien to bring an action to require commencement of a deportation proceeding, see Soler v. Scott, 942 F.2d 597, 601 (9th Cir.1991), we have never held that a delay in commencement of deportation proceedings after a conviction is a defense to the deportation.