Warren Buffett bought $2.1 billion worth of Bank of America stock over 12 straight trading days. It could be years before the billionaire investor and Berkshire Hathaway chief sees a material return, experts said on Wednesday. "He could buy it for another 12 days, he can't really fix the headwinds that are challenging the banks," CNBC contributor Joe Terranova said on "Halftime Report." However, Wells Fargo analyst Mike Mayo said on CNBC's "Trading Nation" that Buffett is "on the right track" as bank stocks could rebound 50% over the next 18 to 24 months.