What is the theme in Smiles to Go by Jerry Spinelli?

Ideas about the nature of time, its changeability and mystery, appear several times and in several ways throughout the narrative. The first relates to Will's perceptions of the Brimley clock, which he remembers as always keeping perfect time but which, over the course of the narrative, begins to noticeably slow, a situation believed by Will to be the result of meddling by BT. The second relates to his own impeccably accurate watch, regulated by a signal from the unchangeable Atomic Clock but which, as Will discovers, is useless when it comes to predicting how long Tabby will be in hospital. The third relates to the climactic "glimpse" across time, of the joy of his long-dead ancestors, Betsy and Andrew, and his simultaneous discover that the contents of the long-wrapped wedding presents can have meaning in the present.