Depends on a lot of things. How many stages, how many strings in a stage (this can be the killer), how many squads/ROs.
So if you figure six stages, and 60 seconds of shooting each stage, you are actually shooting 6 minutes max. The rest of the time you are picking brass, pasteing, waiting to shoot, etc. So, its up to how organized the match is. I have seen only a four sage matce take six hours. And, have saw a six stage match take just an hour and a half. The latter was in Dorr, MI, I couldn't believe how they could do it. I haven't shot there in a few years, this kind of jarred my memory and I should make a point to make it down there next season.