No, a candidate cannot move on to the second section before the end of first 70 minutes even if he/she has finished the first section in less than 70 minutes time. The candidate will have to wait for 70 minutes to finish and then only he / she can attempt questions in the second section.
Can one shift to next section if time is left in the first section?
CAT 2013 is to be conducted by IIM Indore from 16 October to 11 November 2013. Get your questions answered here.