We would always recommend that you seal all Limestone paving directly after installation. Ensure that you use a water based impregnating sealer that will still allow the stone to breath and allow for the natural process of efflorescence to take place. Limestone paving is naturally porous, and this must be maintained or you can cause damage to the surface of the stone. Always make sure your paving is completely dry before sealing and that you have at least 24 hours of dry weather ahead after sealing has been completed to allow the sealer to cure.