how to calculate the timeperiod spent on L1B visa

[master123]

I am currently on H4 visa. I entered this country on June 2007 on L1B visa . We applied for H4 visa on April 2012 and H4 receipt date is April 26,2012 and H4 visa got approved on July 2012. I went out of USA couple of times during June 2007 to July 2012. 

Now, I found an employer who is ready to sponser H1 for me, they wanted to know how much time is left on working -visa out of my 6-year duration.

Question 1: If I am calculating the total time-frame I spent on L1, is the time persiod starts on H4 receipt date or H4 approval notice date?

Question2: Considering my situation, what is the good time to start Green Card in order to continue my stay on H1B (after I convert my visa from H4 to H1)

 

Please suggest.