BuddyPress.org

Ok, after some search, I decided to do this. I found this plugin:

http://www.ringofblogs.com/2007/12/21/wpmu-new-blog-settings-plugin

and uploaded in mu-plugins folder and changed the

add_option(‘gmt_offset’, 2);

to

add_option(‘gmt_offset’, -5);

It seems to work. I had to change the existing blogs to UTC-5 manually.