3 Days: You can appreciate the city at breakneck speed. Allow a half day each for Plaza de Mayo, El Centro, San Telmo, La Boca, Palermo, and La Recoleta. If possible visit La Recoleta on Saturday and San Telmo and La Boca on Sunday to browse their respective markets. Plan museum time in advance as opening days vary, though shops tend to be open seven days a week. Schedule time for an evening siesta to allow you late dinner and a lengthy night out at a club, bar, or tango hall.
5 Days: With five days you can enjoy all the sights listed in the three-day itinerary above at a more leisurely pace. You'll also have more time to tour the riverside promenade of Puerto Madero or head north to the neighborhood of Belgrano.
7 Days: With a week you can fully enjoy all the sights suggested in the three- and five-day itineraries above and venture beyond the city. You could take a day trip just outside town to San Antonio de Areco or up the river delta to Tigre. A day trip to the picturesque and historic city of Colonia del Sacramento, Uruguay, 45 minutes away by ferry is also another option.
10 Days: Spend six or seven days touring Buenos Aires and its immediate environs. Then add on a two- or three-day trip northeast to the breathtaking Cataratas del Iguazú (Iguazú Falls) on the border with Brazil. Alternatively, you make a three- or four-day trip west to Córdoba and/or the wine regions of San Juan, Mendoza, San Rafael, or San Luis.