As long is it is covered tightly with no air getting in, it will last just as long as it would unopened...the longest I have had a roll in the 'frige after opening is 2 weeks and it is still so fresh...I keep the wrapper on and peel it back just as much as I need to cut off a wheel for feeding, AND I put it in a zip lock bag, this keeps it from drying out. If the edge of the roll (where I cut off the wheels) gets dry, I just cut off a slice to get to the part of the roll that is not dry!
There are also directions and info about freshness on their website
http://naturalbalanceinc.com/products/DFRolls.html