Yes, two hours during the day is enought time for your Niemeyer architectural tour. You will be somewhat rushed, but it is possible. I did exactly what your are interested in doing back in 1971, but scheduling with a local tour operator sounds better. I have returned many times since on business, and the details of the actual early construction (helicopters ferrying concrete and brick loads due to the lack of adequate roads) is still amazing to hear.

One word of caution: Brasilia is a "new" national government town, created for that purpose. It would be as though Canberra would be located tomorrow in the middle of the Outback. Little existed there at all before the idea of creating the new national Capital of Brasilia began.

Although conditions (restaurants, hotels, nightlife) are improving, there is not much to do there when compared to Sampa, Rio, or other cities with more of a history. Consequently, the local airport on Fridays is packed with outbound traffic, as government and business representatives and families fly to Rio and elsewhere to recreate and essentially escape. The airport return traffic with the same passengers is crowded Sunday nights and Monday mornings.