as soon as your finished for the nite/are sobre enuff.
even if you leave it til the next morning, which ive often done, cos if you look up on the mirror you'll prolly see lots of coke particles sitting around on your nose hairs, you'll be doing a lot of good.
after 1 long coke nite, put your head back for a while (as if you were lying down) and you shood get a bitter taste of wots lyring around.. then go clean up while you finish with your buzz.