But what if there was a fifth? What if Maeve also attacked during Proven Guilty, sending energy forward to land simultaneously with her planned future attack?
It'd fit the thrown stone analogy, it'd give Harry something to do while there, it'd link the two times we saw time dilation, and it'd explain how Mab knew when the trigger had to be pulled on Maeve's last redemption offer.
I'd be happy with that, though as Raidem pointed out, the amount of energy involved required closer temporal proximity, according to Odin (Woden? Wodanaz? Vadderung lacks familiarity, so I've often wondered why he doesn't present himself as Odin—don't the old gods gain in power by spreading stories about themselves? Or am I confusing Vadderung with Wednesday again? Guhll-dang-it, I read too much).
Still, I could actually see Maeve in Proven Guilty traveling forward in time to augment her future attack on Demonreach, and Harry being forced to stop it from happening.
Alternately, and to possibly make it fit with Vadderung's explanation, Maeve was attacking
from Proven Guilty's timeline (while Mab was distracted with other things and Lea was on ice) at a point in Demonreach's timeline that was within a few hours of the Cold Days events. So yes, the attack is coming from within a day of the events, but the punch is being thrown years in advance.
It always bothered me why Maeve and Lily waited to do their assault until Harry was alive and kicking. It never made any sense. Why not do it while Harry was a ghost (I get it, Mab was on the island), but they've had years to do it from BEFORE Harry was even the Warden. I've always kind of assumed that Harry claiming Demonreach and personifying the island's genuis loci made it stronger (cuz now it has a Warden), but also made it vulnerable, since now it's a physical thing that can be assaulted, if that makes sense.
Even if you accept that it had to be done on Halloween (because Maeve also wanted to kill Lily, or the attack required it for some other technical reason), there were several Halloweens' worth of missed chances, and a few shots at it before Harry was awake.
Therefore, I propose the following:
1. Maeve saw that Demonreach would have a Warden in the future. This would allow an assault to actually have a chance to succeed.
2. Maeve's infection was discovered by Mab somewhere around Proven Guilty. I believe she was outed by Lea during one of her lucid periods.
3. Maeve, realizing that she wouldn't have much of a chance to do something as big as blowing up Demonreach with Mab looking over her shoulder so closely all the time, hatched a plan to hit Demonreach from multiple points.
4. With Mab distracted by the events of Proven Guilty, Maeve took her chance and sent her attack, whatever form it took.
5. This locked Maeve into her tight timeline; she had to initiate her other attack within a certain timeframe of the one she had sent, so she manipulated events as best she could in order to keep the Warden dead. She thought she might've succeeded until he showed back up in Arctis Tor, but by then it was too late to change her plans.
6. Cold Days happens.
I think that might work, but what do I know?
Also... who summoned He Who Walks Before? Did we ever get an answer to that? Because I sure as heck don't remember it.