As stated in the title, tested in singleplayer with wandering trader brains, in both a stasis chamber and a sample freezer that was in a -3°C biome (to remove any chance of accidental lack of cooling). Both blocks worked perfectly when I teleported to 1000,0,0 and back (spending some time there to give the brains some time to start ageing), but seemed to allow their contents to age as if they were mundane storages when I went to the Nether or the End (I didn’t time how long I spent in the other dimensions, but the spoiling timer change matched the likely duration as far as I could tell).