Yes, I'd like to know the specific number of hours too. But aparently it wasn't a lot. In fact it was less than other cases. I saw this quote:
Also, it was described in one article that Roberts time spent was actually playing the role of Justice Scalia in a mock SC hearing.
Imagine that, Hogan and Hartson's Pro Bono department (H & H being the firm that Roberts worked for), asks Roberts to help out by playing Scalia in a SC hearing. Sounds to me like Roberts is a Scalia-type and the Pro Bono department knows it.
The White House said Roberts worked on the 1996 case for less than 10 hours and that he always agreed when someone at his law firm asked for help on a pro bono case in his area of expertise, appellate and Supreme Court arguments.