The irony of orphanhood
There is an implicit irony that shapes the life of the protagonist. His parents die, which means that he has to experience one of life's most gruesome challenges, the loss of one's parents, without his parental support, and he has to endure radical changes in that same season of life, because he needs his uncle's help to survive. He goes from being a dependent person to a severely tortured person trying to make the best of a life he did not ask for.
Magic
Then one day, he sees something that changes his opinion forever. He sees his uncle doing magic and he realizes that magic is unlike anything he'd considered before. This is dramatic irony in full swing, because the drama is that he feels hopeless and bored by life, knowing too much about pain and death, until he realizes that magic runs in the family. In light of that one single change, all his ideas about the natural world fall away and he begins to feel a new excitement for life.
The ticking of the walls
Another clever use of dramatic irony is the ticking walls. Walls don't usually tick, so the situational irony is enough to drive Lewis crazy, along with his uncle Jonathan. They try to drown the sound out with clocks, another clever use of irony, but they cannot cover the sound. No one knows what the sound really is, so there is drama through irony, but more there is something important than what the sound actually is—what does it symbolize? It symbolizes their knowledge of time (because of the loss of Lewis's parents) which is unignorable and against which they are powerless.
The magic of timeliness
When Tardy (whose name is a relationship to time, notice) asks Lewis to do magic, Lewis claims responsibility for a lunar eclipse, and Tardy disbelieves him. Then, they go to a graveyard on Halloween where of her own accord, Selenna is going to rise from the dead, but just by ironic chance, Lewis happens to be claiming magic powers to raise the dead. The irony here is a technical kind of irony called synchronicity where Lewis's vane attempt to prove his magic aligns with the rising of Selenna from the grave—his magic is that he is always on time, unlike Tardy.
Saving the world
To save the world the trio of character has to kill the bad guy (classic storytelling) and they have to destroy a giant clock. The irony here is that they save the world from the clock that will end the world, but of course, they don't really save the world from time. Their fantasy victory is pointing the reader to consider the irony of "saving the world," because in the end, time wins anyway. Of course Lewis wants to believe he has conquered time, but time continues and they get older anyway.
