I think it's an interesting question. Generally, there is no 'wrong' time to enhance your muscles. There are however 'smart' times. Taking D-bol as a kickstart with a long ester cycle makes sense. Taking it mid-cycle as an extra boost - unusual, but frankly, why not? Not the smartest time frame but you'll gain more than if you didn't. Like the old 'pyramid' cycles.
Lastly, end-cycle, again: more gains in doing so than when you wouldn't; if you don't mind d-bol sides like bloat etc, but then again, the idea is to determine timing, not usage, so you're already accepting the dbol sides.
There are also some interesting cortisol-supression theories floating around that would favor end-cycle d-bol.