You can heat gun as soon as you want, it's a little easier while they're stll warm but set up, or you can do it a couple days later. It helps to poke holes before or during to fill in other holes you can't see. Trying to cool them slower seems to help with the sinking sometimes. I do use C3 and use 3 different wicks: LX, HTP, and RRD. Whichever gives me the best burn for the jar, pretty much. I seem to notice they cool on the bottom first then the top, but there are so many variables and things to try, it's definitely worth trying. Just curious...did the vybar help with the bubbles? I have the bubbles too but it still seems to burn fine. If C3 continues to frustrate you, you could try another wax and see if you like it better.