I've already got about a full day of work or so on mine and it's only really the dome, cheeks, and the mandibles/rim that are painted so far. Oh, and the dent is silver. To be fair, though, much of that was trial and error with colours. I think I repainted the dome/cheeks about 4 times before I just gave up and ordered some panzer olivegrun. Normally I'm pretty good at mixing colours, but that one just wasn't happening. I tried twice to get the oxide/boxcar/whatever on the mandibles, but I'm happy with it now. So, part of what will affect the time/difficulty in painting a lid will depend on things like that. In reality - assuming I had exactly the colours I needed to start with - the painting time should have only been maybe a couple hours so far.
I agree about the topical vs layered methods. Topical is easier, but less awesome up close. Layered is awesome up close, but very involved and takes rather longer to do. If you're happy with something that will look great from a few feet back then you might want to consider topical.