Gregorian calendar
Philip II of Spain decreed the change from the Julian to the Gregorian calendar, which affected much of Roman Catholic Europe, as Philip was at the time ruler over Spain and Portugal as well as much of Italy. In these territories, as well as in the PolishLithuanian Commonwealth (ruled by Anna Jagiellon) and in the Papal States, the new calendar was implemented on the date specified by the bull, with Julian Thursday, 4 October 1582, being followed by Gregorian Friday, 15 October 1582. The Spanish and Portuguese colonies followed somewhat later de facto because of delay in communication.

Q: Why did the Spanish colonies lag behind in adopting the calendar?
delay in communication