This was presumed to be because they had to consider they were supposed to hold a series of Imperial events (Crown Prince, Imperial Prince Yoshihito to succeed to the throne and become the new Emperor) on the day when the Emperor died.
これは建前上、崩御当日に（皇太子嘉仁親王が践祚して新帝となる）一連の宮中儀式を執り行なったということにせねばならなかったからだと思われる。