Two videos below, the first has an accompanying timestamp. The first video is on hardcore, but utilizes the infinite rocket launcher and coins. The second one is on assisted, but It's done without any shop items. Both runs take ~1:10:00
An S rank completion requires you to complete it in 2:30:00 or less. These runs give you almost an hour and a half of wiggle room The other factor is to save 5 times or less. Since auto save is active on these difficulties, you actually don't have to save at all.
Run 2 Introduction - 1:12:10
Sprinter, Sensational Work!, Survivor, Veteran - 1:12:57-2:21:35