Earlier, the Brazilians said they were basing their search round Fernando de Noronha (maybe because they had aircraft there) - but there were also reports that the incident was about 300km from Natal, which is in the same area.
I think they probably started searching from Fernando de Noronha as this was the last place where radar contact was made according to the Brazilians.
The timeline as I see it in GMT would appear to be -
2200 GMT AF447 leaves Rio
0133 GMT Last radar contact made with AF447 at Fernando
0214 GMT Automated signal sent by AF447 at unknown location and no further contact
0910 GMT AF447 due at Charles de Gaulle