Digicameinfo shared the image of an invitation sent by Olympus Taiwan. It confirms that the new E-M1 and 12-40mm lens will be announced at 14:00 (2pm) Taipei time on September 10. To make it easy for you these are the other time zones for major cities:
22:00 (10pm) September 9 in Los Angeles
1:00 (1am) September 10 in New York time
7:00 September 10 in London time
8:00 September 10 in Berlin time