Rehabilitation for cancer treatment should start at diagnosis  for best outcomes. this is a research based fact, especially for lymphoedema. "Another appointment" in an often emotionally turbulent time is well worth spent for the future.
Best practice involves referral to appropriate providers for assessment and education pre treatment.
Education of the medical professionals involved with cancer diagnosis to the importance of pre-op assessment is ongoing. 

"Multi-modal prehabilitation requires an interdisciplinary approach, as it proposes a shift from the current healthcare paradigm. The challenge is to recognise that the pre-operative period represents an opportune time for preventative intervention, and to fully utilise this period in order to promote more effective clinical care." (https://associationofanaesthetists-publications.onlinelibrary.wiley.com/doi/full/10.1111/anae.14505)