I don't know exactly how long it takes.
I hearded that the epsons salts ( which are supposed to relax the bile ducts) work for about 4 hours.But the ducts may stay open for a little longer.
On the first day after the flush I am now don't eat any fatty foods, from the second day I start slowly to increase the amount of fat. On the fourth day I eat normally again.
This might not be neccecary for everyone, for me it works fine and feels safe.
Take care, Fellowflusher