same time same place. a couple of things that help, usually you can catch one or two bugs in your hat as they fly around you. grannoms have a darker abdomen, olive in color, greenies will have a bright green abdomen almost chartreuse in color. if you get lucky you may catch an egger. green or red egg sac respectively.

the other option is to shake the bushes along the stream bed and see what pops out. if caddis are present some should fly out of the bush as you shake it. im not a bugologist, so I don't know how many days they spend in the bushes along the stream bed after hatching, but if you don't see any when you shake the bushes,you probably don't have a hatch going on.