Father diagnosed with shingles on side of his face? When do blisters break?

My father has shingles on the side of his face and eye. He has the blisters and is taking medications prescribed etc. for about three days now, but the blisters do not appear to be ready to break. His doctor said they caught it very early. So do the blisters HAVE to break or since caught early they will not, but does that mean it will prolong his recovery?