H1B amendment from part-time to full-time

[m_g]

Hi,

So, i am working for a cap-exempt employer(A) as full-time. I got an offer from cap-non exempt employer(B). Company B wants me to start ASAP so they filed for a concurrent H1B which in the form says to be counted under cap-exempt category from 30 september 2011 - 30 september 2014. Now, company B told me that they are in the process to file an amendment of this concurrent H1B to make me full time with them and they will be filing this amendment on October 1st 2011 which is my start date but it is a sunday (but will get the LCA approved for full time before that). So they asked me to start full time with them from October 3rd 2011.

My questions are:

1. Since my start date is from october 1st 2011, can i join company B after filing an amendment of the concurrent H1B(which has option of numerical limitation as CAP-exempt) to make the hours from part-time to full time and count me under CAP, just having an approved LCA for full time with them?