I was one of first to start using DAP, that was a few years ago. Ive used it on probably 30-40 batches, heres my take:
1) I use it sparingly, maybe a level tsp at most, or even 1/2 of that.
2) Its like fertilizer, it doesn't matter when you add it, really its just a nutrient.
3) If you add too much it will taste and smell slightly sulphury at first, even that will go away (most all of the time) with a little time.
The stuff is great, if you use sorghum as a base and proper brewing techniques fermentation temp etc you will get a nice tasting beer. Its gonna be dry as its the nature of sorghum, but there are other ways to get around that too.