Where will Faber be going on the 5:00 a.m. bus?
The answer to this is that Faber is going to take the early morning bus to St. Louis. He is going to go there to see a retired printer that he knows. Presumably he will see the printer about getting some books published.
Faber tells Montag this after Montag has come to his house for the last time. Montag has killed Beatty and run away. At Faber's house, he drinks the stuff that will disguise his scent from the Mechanical Hound. Then he starts on his attempt to evade the police long enough to get out of the city.