When before natural adhd remedies start to work?

Never: There are no known "natural" remedies for adhd. Some studies have looked at omega-3 fatty acids and at restricting artificial dyes on food but these have been small studies and the results have not been great. The only useful "natural" remedy is behavioral modification techniques bit eve those do not work as well as medications.

Depends: If the underlying cause of adhd symptoms is diet, then changing the diet would make the symptoms go away quickly. If the cause is allergies or learning problems, treating the allergies or learning problems will take longer.