I've used with harmala and without, onset is about 5-10 mins. With harmala it lasts longer and the comedown is drawn out much longer. The experience with harmala was excellent, I did not push it to breathrough doses though, most of it was done as experiments, but breathrough should be possible if it is concentrated enough and the technique of inserting is refined.
If the nose starts to run it will sting if any fluid reaches the entrance of the nostril because the skin is sensitive there.
Getting the right balance between acid and alkaline is the main problem with this method. I suppose if you started with freebase and only added a few drops of vinegar till it all dissolved it would be easier.
Because the acetate is sticky it helps to squeeze the nose after insertion to spread it around. You have to get it quite high up, and don't add too much bicarb else it will freebase and burn more. I originally thought bicarb couldn't freebase dmt-acetate but after using it in my mouth I am convinced that it does. Maybe not all of it, but enough so that it will burn a lot. You should just add enough till the acetate stops bubbling. If the acetate is very liquid you can boil off the vinegar by putting it in a spoon and holding over a flame till it starts bubbling (just don't let it start smoking).
In contrast though i think it is more efficient to use via the mouth with harmala's. Not under the tongue, as the saliva messes with the absorption, but via the space between the lips and gums. You can take more in and the overall absorption seems to be better to me. I've had to use far less and have gotten closer to a smoked experience than with any other method. I made a post about it
here. But if you want to use it without harmala then nasal is the way to go.
Considering how much damage the freebase does to one's mouth and nose it amazes me that people are smoking it so freely.