@Mains-2013 Candidates:
Last date to fill online DAF =extended to 17th September (Tuesday of Next Week)
Last date to send DAF+documents to UPSC= extended to 25th September.

Long story:  Result of Civil Services (Preliminary) Examination, 2013 has been declared by the Union Public Service Commission on 2.8.2013.  As many as 14959 candidates have been declared qualified for admission to the Civil Services (Main) Examination, 2013. As per original deadline, all those who cleared CSAT 2013 (prelims) had to submit their Detailed Application Form (DAF) for Civil Services (Main) Examination, 2013, through online latest by 10.9.2013 and thereafter, they were also required to submit a hard copy thereof along with relevant documents by 18.9.2013.

But some candidates have represented that they could not register/submit their on-line applications, therefore, Commission have decided to allow submission of online application upto 17th September, 2013 (1159 PM).  The candidates who could not submit their online DAF earlier may submit the same latest by  17th  September, 2013 (1159 PM).  

The printed copy of DAF, duly signed, along with all the relevant documents (including prescribed fee, wherever applicable), may also be sent immediately addressed to the Under Secretary, Civil Services (Main) Examination, Union Public Service Commission, Dholpur House, Shahjahan Road, New Delhi 110069 so as to reach the Commission’s office on or before 25th September, 2013 (5:00 PM).   

Ref: http://www.upsc.gov.in/exams/daf/daf_csm2013.htm