How long is it supposed to it take for a unpopped blister to heal?

Not long: Depending on the size and cause anywhere from a few days to a couple of weeks.

Fast Healing: With injury to our skin, inflammation occurs which means the area becomes red, warm, tender and with swelling. Swelling occurs under the skin layers and causes them to bulge creating a protective fluid cushion called a blister. As the area heals, the fluid will be resorbed or when no longer needed, the blister opens and it drains. This should take about a week. Keep it covered and protected.