any one can ask for premium processing at any point of time, i dont think the premium processing will increase the possibility of getting rejected. Like i said in the previous thread created by you, one of my buddy applied without the premium processing got RFE and then applied for premium processing. He got the answer after 3 weeks, the only down side of it was he got the h1 for only 1 year. Hope this helps you and Good Luck.
P.S. ask the attorney how much it costs for premium processing and if you can afford it pay it out of your pocket.