I'm not sure what q6 is supposed to mean.
q6h means every 6 hours, but without "h" I have no clue. 3g Vitamin C every 6 hours is crazy and this could cause issues with kidneys. Even 3g per day is a very high dosage.
It's not a typo though, because it's mentioned like that several times.
It can't be every 6 days, because that would make no sense.