I looked at the memories and couldn't find any sort of answer to this, it's probably not much of an issue but I was just curious.
It's recommended, before using any dye on brushable hair to not wash the same day to give your natural oils a chance to coat your scalp again to protect it from the chemicals. The majority of people with dreadlocks wash their hair less often than people with brushable hair, and it seems as if having slightly more oil, assuming you had a naturally oily scalp to begin with, doesn't seem like the best thing to get hair dye to set properly.
As long as you're giving your head enough time after actually put the oil that was stripped away, does it matter when you really do the dyeing at all? And if you're doing more than one dyeing, do you do it in the same day or give your dreads some time to recover from the first?