Can. 917 A person who has already received the Most Holy Eucharist can receive it a second time on the same day only within the eucharistic celebration in which the person participates, without prejudice to the prescript of ⇒ can. 921, §2.
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Can. 921 §1. The Christian faithful who are in danger of death from any cause are to be nourished by holy communion in the form of Viaticum.
§2. Even if they have been nourished by holy communion on the same day, however, those in danger of death are strongly urged to receive communion again.
§3. While the danger of death lasts, it is recommended that holy communion be administered often, but on separate days.
I have read elsewhere that the day in this case is midnight to midnight; so Saturday evening does not count toward Sunday.