I'm running it now. In general, it takes about one session per year--year 1 took 2 sessions, but included character generation and the into-module from the base book. As +Doyle Tavener
said, be prepped to improvise. The GPC is not a traditional module--it's more of a "here are things that are happening while the PK's go on adventures"--so, even during the railroaded Uther phase, a LOT of what happens is up to the PK's and the GM, not the module. Some of the best parts of the game so far have been when we went off script and explored more personal stories. Now, for me, I love randomness in my games, so I grabbed a bunch of the forms that are out there for random background and downtime events, but pick and choose what works best for you. Good luck!