H1B filing during OPT(ZT)

Can H1B be filed anytime during OPT ?

My OPT is from 5/04 to 5/05. HR admitted to file H1B for me, but said it could not be filed until 6 month before the expiration of my OPT according to the company 's attoney. I don't think that is right. but i could not find any official document to disprove it. I really want to have H1B in hand ASAP. I am sure it could be filed as long as i have an offer ( i have been working here through my one year CPT ).

So please help and thanks a lot in advance.