42 C.F.R. § 418.21
(a) Subject to the conditions set forth in this part, an individual may elect to receive hospice care during one or more of the following election periods:
[55 FR 50834, Dec. 11, 1990, as amended at 57 FR 36017, Aug. 12, 1992; 70 FR 70546, Nov. 22, 2005]