We arrived to BA at 7am in the morning and had just 2 days to see the city. So we got to the Plaza San Martin for 2pm that day, and met up with Bike Tours, who were there from about 1.45pm. It was mid-week.
It was a group tour, from 2pm until 5.00pm, however it was only the 2 of us on our tour, so in effect we had our own private tour! It was fantastic. We chose to do the South tour, which included San Telmo, La Boca, el Parque Ecológico, and Puerto Madero. We highly recommend it. It is a great way to see the sights, without the time it takes to walk everywhere, and without the time you lose in BA's mad traffic on a tour bus.
Our guide was fantastic. He was extremely knowledgeable and it was a really great way to spend our first day in BA and Argentina. At La Boca, we parked our bikes for 30 minutes and our guide looked after them whilst we were free to wander, take all the photos we wanted, and be able to hop back on our bikes when we had had enough.
We were extremely pleased with our choice of activity for the day, and I have no doubt that this tour is on a par or higher with the other companies offering the same service but at a higher price.