L1-B Petition validity

[chandrashekhar_w2k]

I have a valid L1-B (individual) petition from Sep'04 till Sep'07. I had visa only for 1 year, till Oct'05. I came back to India in April 07 and had new visa on the same petition. My visa & petition is now valid for 4+ months. I came to know that I need to travel back to US few months before the expiry of petition but I don't know how many.

Does anyone know this restriction is there for sure ? If so, how many months (before the petition expires) I would have to travel back to US ?

Thanks,

Chandrashekhar