I tried to find a way to do this not too long ago. I sometimes use NVDA to perform poetry I've written at my poetry readings, but the answers I received were that the length of pauses is not controlable via NVDA, it is dependent on whichever voice you are using.
You basically have the length of a comma and the length of a full stop / period, and that's it. I do not detect any difference in the length of pause for a semicolon compared to a comma. There is no way to use two full stops to get a double length pause, nor to combine a comma with a full stop to get like a full stop and a half of pausing! Likewise, with my preferred poetry performance voice, Hazel (Microsoft SAPI5) there is no raised intonation to indicate a question mark, where in other voices (Microsoft Zira, for example) the question mark is clearly audible.
I used to own a pair of Orcam glasses and ran into the same problem with the length of pauses with that system. Just the comma / semicolon and the full stop were the only two pauses. Dashes, m-dashes and n-dashes produce no pause at all in any of the voices I've tried.
One thing that made me smile was that I'm scheduled to read in Torquay, south England, in October and on the flyers my event is listed as Giles and Hazel ... maybe I can make a case for Hazel getting an appearance fee too ;)
Sorry not to have better news on the pausing question. I remain hopeful that one day a solution will be found for this, but I think it lies in the hands of the creators of the different voices.