Mine dried out and became less aromatic in a few months, but that was just the surface. If I chipped another shingle off, only half of the first one would be pale and less scented. The whole log (or branch - the heartwood was mostly only 2-3 inches thick) would hold it's internal oils for at least a few years.
I could split them thinner than I needed. To serve as a 'frying pan" for a bead of resinous incense, around 3-5 mm thick was good. That gave plenty of 'cedar' scent before the incense began to boil, and it lasted longer.
