The most common opening hours for car hire companies at this airport are:
Sunday: 06:00-22:45
Monday: 06:00-22:45
Tuesday: 06:00-22:45
Wednesday: 06:00-22:45
Thursday: 06:00-22:45
Friday: 06:00-22:45
Saturday: 06:00-22:45
You'll find more details about the exact times during the booking process.
If upon arrival at Buenos aires you wish to purchase additional services or must pay any outstanding charges, you must do so in the currency of Argentina, which is ARS.