Sous-Vide Chicken Thighs - Effect of temperature swings?

I think your temperature range is good. 155 to 160 is a good place for thighs. You will need an hour to an hour and a half. As long as you don't drop into the danger zone you will be fine. You could just check a thigh with a probe thermometer at the end of an on-off session to see where the temp is. Sounds like a bit of a pain, but certainly doable. One caution...that looks like a small pot. If you are doing more than one or two thighs, you will crowd the bag and might not achieve even cooking...this could create a danger if the center of the package did not reach 140. Advice: Get a circulator! If you enjoy eggs, for example, the price is worth egg cookery alone, in my opinion. :-)

By the way, while many people prefer this route toward fried chicken, I actually have had the best success with, and prefer Keller's Ad Hoc recipe.

I say resist the temptation to up the temperature. Some other questions here suggest no higher than 60ºC (140ºF) for sous vide chicken in order to best preserve the texture. Granted, that's for breast meat, and thighs will be more forgiving, but you've also conservatively got about 10ºF variance around your target temp. I'd say stick with the recommended 65ºC (149ºF, call it 150ºF) given in your linked resource. If you're confident that you can maintain a variance of less than 10ºF, this will juuust keep you out of the danger zone, and will keep you from accidentally getting too high above the target.

You don't want the sous vide too high because you'll be frying these immediately afterward; by the time you get a nice crust, the internal temp will easily make it up to the USDA's safe minimum if not several degrees higher. If you prefer them more well-done, it's much easier to adjust your fry technique than it is the sous vide. Undercook them, and you can fry them a little longer to compensate; go too long, and you're screwed if you want to get a nice crispy crust with a juicy interior.

That all said, I quite like @moscafj's suggestion of skipping the sous vide if you don't have a proper circulator, and using another recipe instead (Keller does it well, although I think I've used a slightly different version, out of the Ad Hoc book). Switching a rice cooker on and off manually for 4 hours sounds like a real chore. If so inclined, you could hack together a DIY immersion circulator, and/or use the PID controller to turn the rice cooker on and off for you.

Dark meat should be cooked to at least 165°F to break down the connective tissues. I usually shoot for 170°F. White meat is marvelous at a considerably lower temperature as already mentioned. That is why cooking them separately is highly recommended. Finish off your meat under the broiler or on a grill to give it a better flavor, but use a high heat and a short cook time so you do not raise the inside temp much. If it was sous vide cooked to perfection, then you can shock cool the meat a few minutes in ice water before finishing it off on the grill or under the broiler to prevent overcooking the interior.

I cook chicken thighs sous vide at 65°C for 90-120 minutes and they come out entirely suitable to my taste. I could probably go a little cooler, actually. I don't think you want to go super long because the meat becomes very mushy and unpleasant when you overcook it - remember, this kind of cookery doesn't overcook with temperature but with time, although usually quite substantial amounts of it. Four hours might be too long though - I've never done thighs for longer than two.

So you should be fine with two hours with your setup, maybe three, provided you don't let the temperature get too low at any point. Going over risks drying out the meat more than your target temperature would usually do it, but I don't see that a 10°F range is likely to be much of a problem. The reason sous vide is so popular now is not so much because you couldn't do it before as because doing it precisely enough is a real pain in the whatsit.