The calculated distance (air line) between Dayr Ḩāfir and Tadmur is approximately 115 miles respectively 185 kilometers.
By car or train, the actual journey to Tadmur is certainly longer, as only the direct route (as the crow flies) between Dayr Ḩāfir and Tadmur has been calculated here.
Air line (approximately)
185 kilometers
100 nautical miles