There is definitely a delay, how long depends on a bunch of factors such as day of the week and time the feedback is left.
You can do all the analysis you like but it's very difficult to determine the exact dsr anyone has left you.
AT times when I've had very few feedback left such as none for 2 days it's still difficult to detect.
There is a seller on the US powerseller board who insists that they have a tracking system that reveals all but almost every time they try to "prove" it holes in their theory appear.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.