One potential theme of act 2, scene 5, is that anticipation seems to make time move more slowly. Juliet is anxiously anticipating the return of her Nurse, who she has sent to Romeo to inquire about his plans to marry Juliet. Juliet is watching the clock, aware that it was nine o'clock when the Nurse set out, and that the woman promised to return within a half hour; she has actually been gone for three hours now, and Juliet is getting cranky with waiting. Juliet wishes that "love's heralds should be thoughts," which move so much faster than people can do (2.5.4). Three hours is long, but not terribly so, not when the Nurse may move slowly—an older woman now herself—and when she must scour a city to find one young man. Juliet is made incredibly impatient by her sense of anticipation, and this makes the time feel interminable.
Another theme could be, simply, that when youth feel passionately about something, they can forget everything else. Juliet thinks only of her "affections and warm youthful blood," both of which her Nurse lacks, and she forgets to consider the Nurse's health or anything else that might prevent a quick meeting with Romeo (2.5.12). When the Nurse does return, she complains of weariness and talks about how much her "bones ache" from the long "jaunt" she had (2.5.27). Juliet remains impatient and even grows short-tempered with her Nurse, who we know she dearly loves, because she can only think about her own overwhelmingly passionate feelings.