Depends, usually on how far I've gone to fish, especially if there's an overnight involved. If I go to the Salmon River, I'll fish from before sunup to after sundown, or, as my Dad used to say, until the last dog is dead. If I go to Maine to fish with my brother for landlocks, it's an all day thing too. In either case, all day regardless if I'm catching fish. Locally, it's maybe just a couple of hours. Sometimes, when the sulphurs are really on, I'll time my arrival for the start of nymph activity and my departure for maybe mid-spinner fall. I've had a couple of evenings locally when I've nailed several big fish in a short period of time and just packed it in because it really couldn't get any better than that.