i would do it before... but in reality freshwater dip is a poor means to prevent disease... it will kill off some (or most depending on where and what you read) of diseases and paracites that are above the slime coat but diseases such as ICH will not be killed or anything that is below the slime coat as many of these invaders burrow below that point... the best option is to buy a q-tank
but if you do it, as the above is just my openion take it or leave it, i would think that doing it before acclamation would be best...