I cant speak for the corriander, but other spices i have added 5-10 minutes prior to flameout.
dried orange peel i use 10 minutes prior to flameout
as for zest, when i use the zest from oranges i typically use a sperate pot and boil .5gallons of water for 10 minutes, lett it cool to about 170deg, then add the zest (and actual oranges, too) to the .5 gallons, making a sort of "orange tea". i let it sit for the duration of the 60 minute wort boil. i then throw that into primary with the wort and top up to 5 gal. i used the zest from 4 oranges, cut them in half, and threw them in the "tea" in a muslin bag, which also went into the primary.