The double pain will be “once it wears off”
It will be way later
Here it is again. Read all I posted.
Here are the spoilers
"Chopper is going to use a secret medicine from the Mink that will heal Zoro instantly.
- However, when the effect wears off, you will have twice as much pain as you have suffered."
"Zou's secret medicine will give Zoro double the pain he received as exchange of healing him as a side effect."
One says the medicine heals Zoro instantly and will double when it wears off. The other said the pain is exchange for the healing.
Neither two says the pain will occur way later.