Four hours, I'd say. Maybe four and a half to five counting the come-up, and duration increases as dose increases, albeit with diminishing returns when you get to five and a half or six hours (that's like 100mg too).
I can't say as to 2C-C, as I do have some in waiting but haven't used any yet.
2C-B when I suffocated is about equal to 2C-D oral, five hours at most usually, but between insufflated -B and oral -D I'd say 2C-D is still shorter. And obviously if it were also insufflated it would be shorter still, BUT it would likely burn like a live electrical wire sticking into your sinuses. The only reason I can I insufflate 2C-B (my favorite ROA by far for that compound) is that it's the HBr salt, not HCl, so the pain is much less, though still present.
Hey, 2c-d & c are both pretty short & have similar durations. 2c-n is also quite short lived, but there's less info out there on that one. Since this is pretty well answered I'm gonna go ahead & close it.
Feel free to ask follow up questions in the respective threads for these substances though.