couple of issues: you are assuming maeve and lilly created the time warp, and the weapons. I find that assumption dubious; Maeve was the bait, not the mastermind. She was standing at ground zero for crying out loud.
HHWx , who is in Mab's power level is to my mind a far more likely suspect.
second, your concept of time travel is more of the liberal rts type then the hard sci fi type; which works well for some worlds but not as well for Jim's. Conservation of energy exists; its not just the change you have to account for, its the sending the person back to make the change in the first place.
What Odin is saying the farther you send someone back, the more power it takes, and he's also saying its so dang expensive that even people like Mab don't do it- that's why she uses precog instead, where she looks into possible futures and makes changes in the now to make those futures more likely.
which is why Rashid and Mab are far more likely suspects; both can see the possible future, and both had access to the now that was required.
Now you're just being contrary.
First, I'm not just assuming Maeve and Lily created the time warp. Maeve created a time-dilation field in PG, when working with Lily. Then it occurs again in CD, when Maeve and Lily are working together to attack DR across time. When Harry asks who could have done it, Odin Claus says that Harry has encountered this before. Harry then replies that it's one of the Queens, or someone on their level. All of that works together.
Or... we can assume that one of the Walkers, who haven't shown any time-dilation ability, can do it as well. Which is a more reasonable assumption?
Second, I'll admit I'm not as up to snuff on the science fiction protocols on time-travel. But we've seen at least 4 instances of time manipulation. One is mostly mental (Lash in WN), two are distortions (Maeve-Lily in PG/CD), and Uriel being all anti-linear in GS. There was no apparent cost to Uriel's stepping out of linear time in GS; at his level, the power required probably is negligible.
So far, you haven't provided anything about Merlin's time manipulation to create the prison. All you've said is that it isn't possible. But since it clearly happened, it must be possible, at least in the Dresdenverse. The Erlking himself admits in CD that time "is a massive force, all but beyond even our control." But by Odin's definition, the high energy requirement is to CHANGE the past. What I'm proposing isn't CHANGING the past; it's fulfilling what will be because it was always meant to be. Someone had a plan for the prison, and Merlin was the tool (as you like to look at it). Merlin cast the wards, but someone else was probably involved in the time aspects of the creation.
In the argument for TTH, the proposal is that Harry could travel back in time by using a time-nexus-bridge-within-a-pocket-dimension on DR. For that argument, it already happened because the two times are the same, allowing him to go back. Therefore there wouldn't need to be a huge expenditure to CHANGE the past. There would merely be the expenditure to create the time-nexus-bridge-within-a-pocket-dimension to begin with. And since it's happened before, in the Dresdenverse, it could happen again, if the NEED were great enough.
