Adding yeast nutrients during fermentation?

I am currently fermenting a half batch of apfelwein. I pitched a whole package of liquid Wyeast. The cider has been fermenting for 3 days. The other day it started to stink like the notorious rhino farts. After research, I found that Diammonium phosphate(yeast nutrients) can help get rid of the stink. My question is, can I add the nutrients in the middle of the fermentation? Or is it late. Also, am I correct in thinking the smell is a result of the yeast being stressed?

I did that once or twice there is no problem.. But is seems I have Crain bancer now lol

Mix it up with sterile water to dissolve it first

OK I'll give that a shot. Thanks guys