I tend to have this cough at night when the air pollution is bad around here. After coughing most of one night about a week ago, I suddenly remembered a remedy I had tried before and it worked. So I looked it up again the next morning.
I found this 4 years ago, not sure where, but I printed it and kept it should I need it someday:
It takes affect almost immediately and lasts for hours. At least for me it does. It may not work for your cough, but so far it's always taken mine right away. A little vial of it costs me just $7.99 at the health food store. I just put 5 little pellets under my tongue. I keep it by my bed and take it when the coughing starts, about 2 am. Nips it right in the bud, as they say.
At least so far it has. I hope I'm not jinxing myself by writing about it.