I've gone between a quart and a half gallon, depending upon how heavy I go. But I often will do touchups year round.
I bought a simple paper jump suit, meant for painters. Surprisingly, I've used it at least 5 times, and it still hasn't torn. Sweat like a devil in it, under any amount of sun; but works well to keep dirt and FF off me. I'll wear gloves also, eye PPE is a good idea.
I bought the FF sprayer. I have both of the "wand" attachments, and used them a couple of times, to get deep into areas; but touchups I'll just use the sprayer. Crevices which don't get lots of splash will tend to hold FF longer.
Half hour is about the time required. Give or take. Longer the first time, successive times one tends to get more complacent.
A great time is when doing tire rotation: I like to put the rear up onto jackstands, pop rear wheels off, roll up front. Take apart rear brakes and lube sliding surfaces. Pull out sprayer, go to town. Jack front up, do tire rotations. If one can, put front onto jackstands and spray up front too (although access may be sufficient with just rear up). Do oil change at same time too, if necessary. Do all this work at once, it'll kill a Saturday morning.