I freeze my maples after I have cooked up a batch. Some will say that they are best straight after cooking, some will say after three days of fermenting in a bucket, some will say use flavours, some will say use no flavours. I have tried all these and have caught carp on all of them! I have noticed that they are slower to produce initially than (say) tigers on my water, yet when they get recognised as a good food source, the bigger fish seem to come out on them.
As to how long freezing, I use mine in rotation so they are hardly in the freezer for more than a couple of weeks. I see no reason why they will not stay effective (and frozen) for a number of months.