My husband is in prison for aggervated assult w/deadly weapon. If this is his first felony offense, what is the percentage time he has to serve?

I live in texas, this happend in May of 2009 he just went in Janurary. He was sentence 6 yrs. and was told by the lawyer he was given, that he will serve 2 and a half yrs. Which % does he have to serve 35% or 50% of his time? We have a child together who is now two. He was the one that provided for our family and it is really difficult without him. I hope to get a helpful answer please and thank you for taking the time to read this.