H-1B visa (Cap exempt) amendment petition (same employer, new dept)

[akshaksha]

Hi,

I work as a postdoc in a research institute and currently hold H-1B visa (non-profit, cap exempt) affiliated with the university's Dept "x".

• My last date in Dept "x" is July 30, 2012, but I have another offer for a postdoc position in a different Dept ("Y"). in the same university.
  
• Since I am transferring from Dept "X" to "Y" in the same university, I have been told that my new Dept."Y" will file for an amended petition, rather than a new H-1B.
  Q1: If Dept "Y" files for amended petition before July 30(last date in Dept "x"), can I start working from August 1st if I had the Fed-ex receipt number? (Similar to how an H-1 to H-1 transfer works). Or, do I need to wait for the amended petition to be approved before I join the job.
  Q2: If my last date with Dept "X" is July 30, and Dept "Y" does not file for the amended petition until August 5th, then to maintain status during the 5 day gap I plan to do a COS from H-1B to H-4 (my husband is in H-1B status). If I pursue this, will Dept "Y" still be able to do an amendment petition on August 5? (To be sure, on August 5 my status would be, H-1B ended on July 30, and current waiting for H-4).
  Q3: In other words, do I have to be in H-1 status on the day of the amendment filing or can I be in a transition period (H-1B to H-4) COS pending on the amendment filing date.
  

Thank you,

Aksha