Where It All Goes Down
Cairnholm Island, Wales, September 3, 1940; Cairnholm Island, Wales, present day
Peregrine's Island
Jacob might be born and raised in Florida, but he ships off for Cairnholm Island in search of the mysterious Miss Peregrine's home for children (he doesn't know they're peculiar yet) by Chapter 3. Cairnholm Island is practically a character on its own, with weather more erratic than any mood swing. Plus, with only one phone on the island and generators that shut down at 10:00PM, it feels like we're traveling back in time even before Jacob actually travels back in time.
The House on Haunted Hill
Jacob is told by the village people that Miss Peregrine's was a home for refugees during the war. But when Jacob finds the house, he sees that it has been destroyed by a bomb. Not what he expected.
Of course, we eventually learn that the house has been sealed away in a time loop, repeating September 3, 1940, over and over again. There is a lot of foreshadowing about this, like when Jacob says, "the house seemed unkillable" (3.117), and he looks at objects that haven't been moved in years "as if time had stopped the night they died" (5.5). Wink wink, nudge nudge.
Out of the Loop
The date of the time loop is significant because it's set smack dab in World War II. Early in the book, parallels are drawn between Grandpa fleeing both monster-monsters (the ones with tentacle faces) and Nazi-monsters (the ones with swastika armbands). When Jacob stops believing his grandfather, he assumes that Grandpa was just making the Nazis into literal monsters: "They were monsters with human faces, in crisp uniforms, marching in lockstep" (Prologue.47). Much later, he realizes that it was both: "[Grandpa] faced a double genocide, of Jews by the Nazis and of peculiars by the hollowgast" (9.58). Double bummer.
Jacob can't imagine what that must be like, "to find yourself in the midst of an otherwise unremarkable afternoon, suddenly in the shadow of enemy death machines that could rain fire down upon you at a moment's notice" (5.180), but he does find out. In the time loop, bombers fly overhead like clockwork, and they drop bombs right before the time loop resets.
This should be horrific, but after you've seen it so many times—and know you'll be safe—a certain beauty emerges to the bombs bursting in air and the rockets' red glare. The peculiar children even call it "our beautiful display" (6.207), which would never happen if their time moved linearly instead of in a loop.