It can vary a lot depending on how much you explore and do side quests. But on average, it might take you around 40 to 60 hours.
Well, the time to finish RDR2's story really depends on your playing style. If you just focus on the main storyline and don't get too distracted by side activities, you could finish it in maybe 30 to 40 hours. But if you want to fully immerse yourself and do all the side missions, it could easily take 60 hours or more.