Does the period of time taken by the Department of Justice during the course of the confession/admission process determine whether the confession or admission was voluntary?

Our Circuit has held that the period of state custody can be considered in determining whether the confession or admission was voluntary. Smith v. United States (9 Cir. 1968), 390 F.2d 401 and Little v. United States (9 Cir. 1969), 417 F.2d 912. However, as stated in Smith, supra, "The determining factor is not the amount of time elapsing between arrest and confession, but rather the nature of police activities during this period." 390 F.2d at 403. Cote, supra, states "Nor is there any evidence in the record to indicate the primary purpose in detaining the appellant was to allow federal officers to interrogate him." 357 F.2d at 793-794.