In the Abbot & Costello "Who's On First?" routine, what is the meaning of "St. Louis has a couple of days on the team?"

This transcript refers to the New York instead of St Louis but the ideas the same.

In the skit the pitcher is named Tomorrow and the catcher is named Today. The team those has two people named like days.

Costello: The pitcher's name?
Abbott: Tomorrow.
Costello: You don't want to tell me today?
Abbott: I'm telling you now.
Costello: Then go ahead.
Abbott: Tomorrow!
Costello: What time?
Abbott: What time what?
Costello: What time tomorrow are you gonna tell me who's pitching?
Abbott: Now listen. Who is not pitching.
Costello: I'll break your arm, you say who's on first! I want to know what's the pitcher's name?
Abbott: What's on second.
Costello: I don't know.
Abbott & Costello Together: Third base!
PAUSE
Costello: Gotta a catcher?
Abbott: Certainly.
Costello: The catcher's name?
Abbott: Today.
Costello: Today, and tomorrow's pitching.
Abbott: Now you've got it.
Costello: All we got is a couple of days on the team.