Fluctuates so wildly as to be meaningless, for me. It's not even consistent with when I'm DMing/playing.
In 2E, I often spent pretty much no time thinking about AD&D except when playing it, or maybe reading an adventure immediately before a session. I spent a lot more time reading other RPGs, and discussing them online, as they tended to be much more interesting to discuss and the people discussing them were closer to my age (most people who wanted to discuss D&D back then seemed to be 30+, where I was a teenager, and with very fixed and very dungeon-bash-y ideas about things).
In 3E, I went from spending huge amounts of time discussing the impending 3E, and then 3E after it arrived for a couple of years, and reading 3E books, and so on, and not playing or DMing much, to playing a moderate amount, but not discussing or reading about it at all, unless I specifically was looking something up.
In 4E, I mostly DM'd, and I did a steady moderate amount of prep work, but it was more like 1-5 hours/session of prep, because it was so incredibly easy. The larger numbers would always be where I decided to type up lots of description, or do really complicated maps (I hate maps, I used to love them when I was a kid, but now I just wish people would do them for me). I didn't discuss 4E all that much online either, outside of a couple of few-month-long bursts of more heavy discussion which actually aligned with times when I got to DM it less.
In 5E, I discussed it for a long time whilst not playing any kind of D&D (unless Dungeon World counts), and read about it a fair bit. Then started running it a lot but not really reading about it, and trying to take similar amounts of prep to 4E, which is sadly not really practical, as 4E was more DM-friendly (or friendly to my style of DMing, doesn't matter which), and I had to take increasingly longer times to prep it. And I wasn't discussing it much when I was running it a lot. More recently, I've been discussing it a ton, and playing it more than I have since, ummm, well, wow the '90s really.
So what I'm saying is it just doesn't correlate well. Even with 5E feeling like it needs a lot more prep time than 4E, if I just ran an AP (which I don't want to), that prep time would be cut massively to just reading the AP completely once, and then re-reading and maybe editing bits of it before each session.