how long???

ok so here is the deal i discovered my plants had a nitrogen dif and i put some coffee grounds and some fish fert... and i was wondering how long will it take before i can see if the ferts are working? i know you can't give me an exact length i was just curoius if anyone could give me an idea of what to look for.
Thanks for any help.

smetimes a couple of hours sometimes day sometimes never it all depends on how bad a def you have