Considering the amenities in Castleton, the walk itself and daytime hours (especially during the months with good weather) would be ideal for picking the “best time” to visit Cave Dale. The walk provides various scenic points, so a clear day will enhance the experience.  Additionally, consider visiting when facilities like public toilets are open (8 am - 5/6 pm) and when the Castleton amenities such as cafes and pubs are operational and maybe less busy, e.g. weekdays and outside of school holidays.