Patient had 3 day inpatient stay at hospital, met Medicare guidelines, and used all 100 days of his Medicare benefit. When will a new benefit period start?

Patient was transferred to the hospital and gave up bed hold. Patient has a Federal BCBS plan that pays 21-30 Medicare coinsurance days. Patient was admitted inpatient and underwent below knee amputation. Patient is needing SNF again but has used all 100 days. Will a new benefit period start at day 1 because he NEEDS Skilled Care again? This is so confusing and need to know so I can plan for his recovery.