It depends completely on the severity of the burn. It could be a few days, or up to a few weeks. Until then, put aloe on the blisters and try not to move the burned area.
A typical burn blister can take up to 12 days to heal. Do not pop the blister due to the fact that it makes the burn prone to infection. Ice it to dull the pain and pad the burn with bandages to...
Cool the area with cold milk to stop the burning, which will reduce the time needed to heal. Keep the area moist--aquaphor, aloe or other lotion-- will help it heal.