I have only one question.... how large are these blisters?
Shingles blisters tend to be small. Burns tend to be large.

A delayed reaction like this, might in reality be a Shingles attack.

Shingles comes after a stresser of some type. Sometimes it is immune, others fatigue, or injury. (my husband developed shingles a week after a bee sting).

It really should be looked at by a doctor, to determine if the blisters are indeed from the burn, or possibly something else.
Shingles can itch and burn and may have clear fluid heads that leak fluid, or sometimes they involute after the blister stage and turn black, after a week or so. If these are shingles blisters, you will need antiviral treatment quickly to prevent permanent nerve damage which can cause substantial pain in the future.