Searching online is a mixed bag -- folks that sound like they know what they are doing are merely convincing, not experienced. [Yeah, I know, I'm some faceless dude on the net telling you want to do ....]
Fining agents can do amazing things! Also keep in mind that CO2 keeps solids suspended, so what you are seeing is a mixture of the two actions, degassing and fining.
"How long?" is a tough question. Because every wine is different, there's no single answer that works.
Watch the wine. If necessary, mark the sediment line with a grease pencil or other wipeable marker. Sediment will build up quickly over a 1 to 5 day period (normally), then it will compact. Let it go 3 to 5 days, or until the sediment level doesn't decrease for a couple of days. The total duration can be more than 2 week, but is normally less.
Headspace is another toughy. The ratio of headspace to wine volume has a lot to do with it. For a 4 liter jug? I'd want the wine within 3 to 5 cm of the stopper.
Contrary to common belief, oxidation does not happen instantaneously. It's a factor of headspace volume vs wine volume AND time. A week or two of a larger headspace is probably not a problem. That said, I keep headspace to a minimum as much as is feasible.
You can top with white wine -- anything lightly flavored will do.
I purchase Carlo Rossi (California) jug wines in 4 liter jugs. The wine is cheap and makes great cooking wine, and I keep the jugs. I also have a large collection of 1.5 liter, 750 ml, 375 ml, and smaller bottles for topup wine. While it doesn't help now, plan all batches for your container size. If you have a 4 liter jug, plan 6 liters of wine and keep the excess in smaller bottles.