F2 to H1b Transfer with Greencard sponsership after 6 years of H1b

Here is my case - If anyone has been in a similar situation and can tell me how much time this will take, will be much appreciated.

1- I have been on h1b from 2004 onwards and and had an approved I-140 EB2 category with priority date of March 2010.
2-Recently i decided to change my job and new employer agreed to take on the GC process.
3- I resigned prematurely at the end of september, before the new company can file and port my h1b transfer. They couldnt get the application ready in time to file and since i had option of a COS to F2, attorney advised me to take that option.
4- I applied for an f2 COS from my previously beyond 6 year extended h1b. F2 is in process.
5- my employers attorney is saying that currently my LCA is under process for last (1month) with website and newspaper ads. I will have to wait till that gets approved before they can file my h1b and take that process ahead.

My questions.
1-How much time should i anticipate for this process before i can join the company and start working again.
2-Could they file my COS from f2 to h1b concurrently as my LCA is under process under premium processing so that i can start working.

Any guidance much appreciated.