Well, the issue I have is if he called me on a Saturday to help, I'd have just driven up and helped, no charge. I don't expect payment for everything I do. A mercenary world isn't particularly appealing. Since I'd drive up on a Saturday, what makes Tuesday different? I also have more fun fixing fence chargers and waterers, than I do staking out wetlands, or some of the other dumb shit I do for money :^D
I'll probably see how the rest of the week goes. I'll start by billing a couple hours. If he pisses me off or something, it's easy enough to bump it up. My timesheets are pretty arbitrary. I account for my time accurately on my jobs since they're all T&M. His jobs are fixed rate for the most part, so I pad here, cut there. If he wastes a bunch of time before heading out, I'll split it up over his jobs, maybe taking a little off if I'm having fun screwing around on the internet or something. I don't worry about it too much.