According to some weeb who posted translated shit
Dragon Ball Z: Kakarot Playtime:— Dragon Ball Hype. (@DbsHype) January 8, 2020
35-40 hours to complete just the story and 80-100 hours including everything (side quests, collecting stuff and etc)
The quality of this content, is of course the most important aspect. But if it's shit, it's a big shit.