How Quickly Do You Flood After Outlining?

Stefani: If you don’t want a line between the dam and the flooding you have to dam and then immediately flood. Otherwise, the dam will be too dry to absorb the flooding icing and that line will show. I’m not much on any “20 seconds, 10 second’s” whatever consistency. I generally thin the icing to a point that it will hold on the edge of the cookie then immediately flood it with the same icing. Then, take a toothpick and even it all out, mixing the dam with the flooding along that edge. I don’t always get an absolutely smooth surface for something like stamping but it generally works for me. Gently shaking the cookie after flooding also seems to even out the surface as well.

When I make a lot of cookies of the same design, I outline all of them first then flood them. When flooding I flood to the very edge of (almost over) the outlines, so that the outlines won't show so much. I think it's important to put enough icing for flooding to get the flat smooth surface.

I agree with all that's already been said. I would add that it looks like your flooding icing was a little too loose (and also thinly applied), so it settled and sunk more in the middle than it has to. Try working with a slightly thicker consistency and doing what the other two ladies (above) said if you don't want to see the outline along the edge.

If I want  a line, I use thicker icing, and a larger nozzle and just take care to make the line really neat.
If I don't want a line, and I'm doing a lot of cookies, I will use a 10 second consistency for the line and a quite small nozzle (eg PME 1.5), and immediately flood with approx 5 second flood, so it will all settle by itself.
If I'm not doing a lot of cookies, and can't be bothered to make seperate icing bags, then I'll only mix the 10 second consistency, and outline and flood immediately, then I usually shake the cookie to settle the icing. If it's a delicate cookie, I hold it gently in my left hand, and 'vibrate' my left hand with my right, if that makes sense? Evens out a whole lot of problems with the flood!