24 hour notice for denial?

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A few months ago I attended a seminar given by Empire Medicare (FI for NY State) where it was stated that beneficiaries must be given 24 hours notice prior to issuing a denial letter. Social worker said today that the regs have changed and now 48 hours notice is required. Does anyone know which is correct and where I can find the reg?   Thank you- Erin McQuiston RN