Live recordings can be recorded in an hour of course. Other artists do significant improvisation, and will release those improvisations as recordings.
The length of time do do the mixing will depend on the complexity of the instrumentation. Nobody seems to complain about the John Lennon/Plastic Ono Band recording, even though it is exceptionally simple. Typically Ringo's drums, Klaus's bass, and John Lennon on either guitar or piano + vocals. Something like that could be recorded and mixed very quickly. And, that was before modern software.
Modern software (I dunno what Neil uses), makes things and order of magnitude easier. If you record with good mics and techniques in the first place, and are not doing anything too experimental, then a compentent engineer and producer should be able to get something that sounds good in the time available. It won't sound quite as glossy as if they could spend a month on it, but do we always want the music to sound ultra-glossy?
Similar for mastering. I've been impressed with the Izotope mastering software. It includes very well designed presets, and just going through the preset browser often resulted in something that sounded pretty good. With modern loudness metering, then getting an overall master where the tracks sound balanced is not that tricky. Again, there may be less of a consistent sound than if someone had a month to work on the mastering, but is this the end of the world?
The music industry is changing. Technology is cheaper than ever before. Returns from albums are less than they used to be, and even major acts fail to make a profit on albums after spending months in the studio. Perhaps it's time for us to accept something home-made because otherwise many artists may not be able to afford to release as many albums. Stevie Nicks says that she will not record any more albums as she can't make money on them. Stevie Nicks!!!!
Bill Nelson records large numbers of albums at home and releases them direct to his fans. I think he releases an album a month, and it's pretty much just him I think. I thought I'd go check out his latest album to show what can be done, but listening to it now (song 'I'm Dancing') the mix could be clearer, particularly the vocals. https://billnelson.bandcamp.com/ Too much 'verb and not enough frequency/pan separation of the instruments maybe. Though, who am I to second guess Bill Nelson with all he's done.
But even then, I'd MUCH MUCH prefer music recorded and mixed like this to no Neil music at all, if that was the choice. Though, I'm not suggesting that this is a financial decision, I'm sure it's an artistic one. It's just intersected with thoughts I'd had on whether more music should be recorded in less expensive ways these days.
EDIT: Belle&Sebastian's first album 'Tiger Milk' was recorded over three days as a Glasgow College course on the music business would record an album each year by a local band. I'm not familiar with them, but the 1996 album sounds reasonably Neil-like in genre (though maybe not so strong on the songwriting front as a Neil album). I can't see that there would be any reason why Neil's album should sound worse than Tiger Milk, and Tiger Milk sounds fine IMHO. Perhaps the drums are way back, but that's not an unreasonable mixing choice.