OMG! Seriously?
Are you a fucking pussy?! If you've set your grow up in such a way that you can't be away from it for more than a day then it's a piss-poor effort. Dude! Just give up if you're gonna be so lame...
Honestly, it doesn't take that much effort to automate a soil or hydro grow, at least in the short term at any rate. Obviously you're just paranoid now that they're big and full of bud. Suck it up! 3 days of darkness will stress the plants. Photosynthesis is a big deal, man. Robbing them of it is not a good thing.