The time that your refill is due is dependent on your pharmacy. You should contact them to find out when your refill is due. Only they can tell you this. Also, you can call your insurance and they will tell you what their stipulations are for how much of your medication needs to be used up.
A prescription for vistaril 50mg reads: take 100mg every 12 hours for 14 days. The pharmacy has 50mg capsules in stock. How many capsules should be dispensed