Tires can be stored for 2-3 years without problems, if done correctly. Put them on pallet if you can, so air can circulate around them. Never store them standing upright, or you risk flat spots. Keep them someplace cool like the basement, not the garage or back shed, as heat will break down the rubber. So will sunlight, water, oil, and grease. Don’t store them within 50 feet of an electric motor, welder, or transformer, and the ozone created by electrical devices will break down the rubber. Don’t keep gas, paint remover, or other strong smelling chemicals in the same room, as the rubber will absorb the chemicals.
I have a spare set of tires laying under the bed in the guest room…they were dirt cheep, and I'll need them about August or so.