Why does “hour” change to час, часа, or часов in Russian?

Russian doesn’t just put a number before “hour” — the word itself changes shape to match it. Час (1), часа (2–4), and часов (5 and up) are all “hour,” but each needs its own number range: в час (“at one”), в три часа (“at three”), в пять часов (“at five”). The same three-way split works for every countable noun in Russian, not just time.

The clip’s own schedule runs through the full paradigm: в час (1), в три часа (3), then часов for five, six, eight, nine, ten — and even в двенадцать часов (12), because 11–14 always take the genitive plural no matter what the last digit is. The same 1 / 2–4 / 5+ split governs any countable noun — один стол, два стола, пять столов (“one table, two tables, five tables”) — so cracking it for hours cracks it everywhere.