The lines in question occur at the very end of scene iv, following Mercutio's famous Queen Mab speech and just before the beginning of scene v which is the Capulet's feast.
Following the discussion of dreams, Benvolio reminds Romeo and his friends that time is slipping away from them and, if they do not hurry, they will be late for the party. Romeo contradicts Benvolio and says that he fears they will be too early and he shares his premonition that their attendance at the Capulet's party will set into motion a chain of events that will lead ultimately to his own death. The audience is aware of the accuracy of this foreshadowing from the information we received in the Prologue. However, Romeo--in true Romeo form--ignores his own fears and better judgement and heads to the party anyway.