We had a VDB (and Cynotype) demo at camera club a while back and I inherited the left over chems. It's been sitting in my cupboard (in mostly darkened darkroom) for months and the other day I finally got around to trying it out.
In our CC demo, we used a UV cooker (box with UV lamps) but I used the sunlight and when doing the VDB in sunlight I noticed something wonderful... I got to watch the reaction... After about 15-20secs the emulsion started changing colour from a light cream/brown to a dark tan. Not knowing what I was doing, and having read a book which mentioned 6-8 mins where required, I left the 1st one for about 5mins but decided that it was grossly overexposed as the image was disappearing, not getting better. The next one I cut back to about 3 minutes and it was much better although my inkjet enlarged negative had defects that showed up in the print. However, overjoyed that I could see something... I decided to stop exposure a bit after I could see that the reaction had taken place (all the emulsion changed to the dark tan colour... this happened in a bit over 1min) This produced the best image, although it's a tad light, especially the 'blacks' I might read up on the toning article mentioned above to see if I can improve it a bit.
Overall though... what a great way to spend a couple of hours