Hitwise just published a new study examining how much time people living in different countries spend on Facebook. Singaporeans actually spend the longest on the social network, with an average of 38 minutes and 46 seconds per session, while people living in Brazil spend less than half that with an average of 18 minutes and 19 seconds per Facebook session for August 2011.

Singapore is followed by New Zealand (30 mins 31 sec); Australia (26 mins 27 sec); the UK (25 mins 33 sec); and the US (20 mins 46 sec). Brazil actually has the highest percentage of Internet visits going to social sites (18.9% of Internet usage) with 43% of all social networking visits in Brazil going to Google-owned Orkut. In contrast, the UK has the lowest market share of visits going to social networks with 12.2% of visits.

Facebook was the most visited Social Networking site in the US in August 2011 receiving 91% of visits among the sites followed by Twitter with 1.92% of visits. Tagged.com ranked 3rd for the first time, passing MySpace.com with 1.04% of US Internet visits.

The fastest growing country in terms of visits is India, which saw an an increase in market share of 88% in August 2011 compared to August 2010. The US also experienced a market share increase from Facebook of 5% year on year.

It’s no surprise that Facebook is seeing major growth internationally and in the U.S. Marc Zuckerberg just revealed that as many as 500 million members have used used Facebook in a given day, which is a milestone for the network. And the social network saw a record number of visitors in July.