Federal prison sentences don't offer a lot of opportunities for early release--you get to shave of 54 days per year of served time, or in other words, he might be able to get out 7 years early were he sentenced for 50 years.
The only way he'll serve less than 5 years is if Trump is elected president and decides to pardon him because no one should go to prison merely for defrauding people out of billions of dollars.