42 C.F.R. § 409.30
Posthospital SNF care, including SNF-type care furnished in a hospital or CAH that has a swing-bed approval, is covered only if the beneficiary meets the requirements of this section and only for days when he or she needs and receives care of the level described in § 409.31. A beneficiary in an SNF is also considered to meet the level of care requirements of § 409.31 up to and including the assessment reference date for the initial Medicare assessment prescribed in § 413.343(b) of this chapter, when correctly assigned one of the case-mix classifiers that CMS designates for this purpose as representing the required level of care. For the purposes of this section, the assessment reference date is defined in accordance with § 483.315(d) of this chapter, and must be set for no later than the eighth day of posthospital SNF care.
(a) Pre-admission requirements. The beneficiary must—
(b) Date of admission requirements. 1
(2) The following exceptions apply—
1 Before December 5, 1980, the law required that admission and receipt of care be within 14 days after discharge from the hospital or CAH and permitted admission up to 28 days after discharge if a SNF bed was not available in the geographic area in which the patient lived, or at the time it would be medically appropriate to begin an active course of treatment, if SNF care would not be medically appropriate within 14 days after discharge.
[48 FR 12541, Mar. 25, 1983, as amended at 51 FR 41338, Nov. 14, 1986; 58 FR 30666, 30667, May 26, 1993; 62 FR 46025, Aug. 29, 1997; 63 FR 26307, May 12, 1998; 64 FR 41681, July 30, 1999; 68 FR 50584, Aug. 22, 2003; 72 FR 43436, Aug. 3, 2007; 82 FR 36633, Aug. 4, 2017; 84 FR 38832, Aug. 7, 2019]