I did 48 hours on two of my plants once, and they turned out fine. I don't really like using a period of darkness before harvest though. I'm sceptical on whether it actually enhances the plants, or if they just seem more taxed with thc because you haven't touched them, and there's no heat degrading the thc. I just try to make sure my plants aren't to close to the light, especially right before harvest, and give them a nice week of flush.
