This.
Lines drop overnight because the sharper players will jump right on them. The public generally plays much closer to game time, so any late money should be taken with a grain of salt.
Line moves are just opinions, they rarely involve some sort of secret information.
I'll agree with you on the opinions/secret info part....hence why I keep saying IF you don't know WHY the line is moving, disregard it or start googling the news alerts to see if anything is there
As for the time of the drops, I'd disagree. The lines move early on, right after they open, b/c the key books that set the lines (Greek, Pinny, CRIS etc that Vegas and the PPH off-shore books mirror lines from) have
a) keyed/flagged certain sharp action accounts
b) have relationships with sharp analytical guys or groups
and they let a) and b) bet these lines before anyone else and then automatically adjust the line based off their selections and then everyone else mirrors these adjusted lines for their opening lines.
Then you have other sharps who want to stay off the grid that will get their action down later on, because they know their spot on the totem pole for how info/accounts are tracked and plays mirrored. So they'll pick a spot closer to the game, to prevent people who try to mirror them from copying their action.
Early line moves are scary to follow b/c you can never rule out a false move and the same group or a rival group/sharp coming over the top the other way.
You also have to factor in what particular game/sport it is (say Clemson vs Louisville in primetime national TV versus a Tue night MAC game or a hoops game) and how much money it takes to move a line. It's extremely volatile depending on those two factors.