Judging from your prints it appears that you used Polaroid PN55 negatives. In my experience PN55 negatives don't have enough contrast for alternative process. If you want to increase the contrast of the negatives you can bleach and redevelop in a pyro developer like PyroCat-HD or W2D2. Be cautious of PMK as it can build too much UV blocking stain.
Originally Posted by buggy
The negatives also look a little over exposed. This will also affect your printing times, aside from the fact that the single UV bulb may lack adequate intensity forcing long prints. If you have a step wedge, print that along side your image negative. This will give you an idea of how your process technique fairs and s if the image negative has proper contrast. The VDB process needs contrasty negatives with a DR of 2.2 or so, up to 2.4. The step wedge will show you what the exposure scale of the process is.
Judging from the dark borders around the image it looks like you printing time is adequate.