I'm with Steve - 48 hours seems really long. How much does your turkey weigh? You have 3/4 cup of salt per gallon in your brine, so it's a little less than I use for poultry (1 cup per gallon), and I brine a 5 pound chicken for about 4 hours. You have a lot thicker meat, and more mass, with a turkey, so I think Steve's recommendation of 24 hours should be sufficient.
Unless you're using an equilibrium brine, time is important. I'd say try 24 hours, then adjust based on the results.
Here's a little something I put together about brines, if you haven't seen it:
http://smokinitforums.com/index.php?topic=1504.0Let us know how the bird turns out!
One more thing... Did you notice if your turkey contains added solution? Many turkeys are "pre-basted" with a salt solution, so be careful if it was. If you brine an injected turkey, you may end up with a pretty salty bird. I have a hard time finding turkeys that aren't injected, and I don't brine them.