My 2 cents:
DBol before training for many gives them a bit more aggression for attacking the weights. Many (including me) got better pumps when taking DBol prior to training. Optimally would be what BBB suggests, but I don't think it is a waste if you take it even just prior to training.
If you are taking other anabolics with the Dbol, then pre-training seems to be the best time based upon many anecdotal experiences from others who had commented on this usage practice.
However, if you are only using Dbol as a supplement (i.e. only using it for a temporary boost for training or recuperation), then you need to experiment to determine whether pre or post training is best for you. Pre-training is still good for the rationale indicated above, but when I did Dbol only (used like a supplement which meant ONLY on training days) I got the most benefit taking the Dbol AFTER training. Using Dbol this way really really cut down on my recuperation time. For me, comparing those training days when I didn't take anything pre or post to when taking the Dbol post was a significant difference. When using Dbol as a supplement in this way, I only used the Dbol on those training days where the volume/intensity was going to be very high.