The calculated distance (air line) between Khān Shaykhūn and Tadmur is approximately 111 miles respectively 178 kilometers.
By car or train, the actual journey to Tadmur is certainly longer, as only the direct route (as the crow flies) between Khān Shaykhūn and Tadmur has been calculated here.
Air line (approximately)
178 kilometers
96 nautical miles