If you were to assume that pascalite clay actually pulled mercury from the body, then a wait of 4 days would be appropriate. That would allow any bits of swallowed Amalgam to pass through the body.
But I don't believe pascalite clay is significantly more effective than the amount of sweating it produces. I have taken whole baths in it, and it is nice for the skin. Right now, I'm a little concerned about the aluminum content, so don't know if I'll be using it much anymore.
If mercury poisoning was localized at some point below the skin, causing a break, then pascalite clay would probably work wonders. Unfortunately, mercury gets pulled into the CNS, behind the blood-brain barrier, where it does the most damage.