Amendment & Miscellaneous
This article and Articles 5, 6, 7, 8, 9, 60, 324, 366, 367, 379, 380, 388, 391, 392, and 393 came into force immediately (on the Constitution's adoption), while the Constitution's remaining provisions came into force on 26 January 1950 - the date this Constitution calls its "commencement".
This explains why India celebrates 26 January as "Republic Day" - that's the formal "commencement" date when most of the Constitution actually took legal effect - while a small handful of specific provisions (mostly citizenship and transitional/procedural articles) had already come into force slightly earlier, when the Constitution was first adopted by the Constituent Assembly.
This is the constitutional basis for why India's Constitution Day/Republic Day is celebrated on 26 January (1950) specifically, even though the Constitution had actually been formally adopted by the Constituent Assembly a couple of months earlier, on 26 November 1949.