Unless you NEED to give them extra darkness, I wouldn't. It wouldn't likely hurt them or anything, but why waste a day? Give them as long as you need to to get them on the 12/12 schedule that you want, but I don't think it does anything beneficial to give them more than you need to.

At the end of *flowering*, there's a theory that 36-72 hours of darkness makes the THC potency increase with some strains. Whether that's true or not I don't know, but I do it anyway just in case it's even marginally true, and it's never done any harm. But I've never given a big dose of darkness between veg and flowering, and everything's turned out fine, so I don't see any reason to even try extra darkness then.