Great question, would like to hear about yours too...but here's mine.
After I released my first product back in 2000 (yikes!) it opened the door to a number of interviews which, at the time, were a little more challenging to record not having all of the digital gear we have today within reach.
I quickly pulled together 3 interviews with top, market leading experts, recorded all 3 interviews in one day, edited them down and had them ready to distribute the next day. It took me another day to complete the sales letter and setup the new product in my shopping cart. That same afternoon (3rd day) I had the product website up and running and emailed my list who snapped it up like hungry jackels.
So, that was 3 days with 1 of those days making up the bulk of the effort.
The product was high quality because the experts were the real deal and the questions were detailed - pulling lots of interesting stuff from them...I still go back and listen to them today.
What about you - what was your fastest product development that led to a quality product?