It has an estimate on there
Well, in my house we've installed it on a 2.4Ghz Core 2 Duo MBP and a 1.3 (I think!) Ghz iBook.
It took a little longer on the iBook, but in both cases, it did take a couple of hours. The first stage - analysing the disc took a fair while, and then when you get into the actual install, you get an estimate of the time... my brother's (iBook) started at around the 3hr mark but quickly came down to about 1hr 45 and went from there, really.
Mine was a bit faster but it still took a while
And yes! It was the Family Pack.
All that aside, everything is smooth on the MBP. It seemed a bit chuggy, turned it off last night. This morning I rebooted it twice and now everything is as sweet as a nut as they say.
Just be sure to let Spotlight index! Patience!