Rockstar Games took eight years to develop Red Dead Redemption 2, and it really shows in the depth and breadth of its world and story. Just the main quest line itself can take days to complete, and there are still a number of stranger missions, collectibles and challenges necessary to reach 100% completion and become a truly legendary gunslinger.
Let's take a look at how long each portion could take to finish. The times listed are estimated, and any player could realistically finish faster, especially if they are speed-running.
Missions and Events
The first section of the completion requirements is by far the heftiest and most time-consuming. In addition to the effort required purely to complete the story missions and stranger missions themselves, there is also a significant amount of travel and wait time involved, as missions can be in different locations or only trigger during certain times of day. It is possible to optimize the completion time strategically, but most would probably prefer to pace themselves and enjoy the game's character work and unique atmosphere.
There is also a requirement to complete five bounty missions, twenty-five side encounters, clear out six enemy gang hideouts and get bushwhacked by a rival gang at least once. Most of these other requirements can be completed fairly quickly, but their random nature makes it harder to estimate a completion time.
Completion: 55-75 hours
100%: 75-95 hours
Collectibles
Tracking down all the required collectibles can take wildly different lengths of time depending on many factors. Since many items and locations are essentially hidden all over the enormous map, a passive player may take dozens of hours to actually find everything they need.
Using a guide cuts down the time significantly. However, there's still the matter of catching all the legendary fish, which requires waiting to hook the fish and playing a challenging mini-game, and painstakingly hunting the animals required to complete Algernon Wasp's tasks and fulfill Ms. L. Hobbs' hunting requests. As a result, skill and luck certainly play big roles in the process.
100%: 20-40+ hours
Compendium
In contrast to the first two sections, the compendium is actually relatively straightforward. Players can complete a significant portion of the requirements by just playing through all the story missions and will inevitably complete a few more by randomly exploring. The wild animal and weapon requirements will probably require the most effort simply due to how many there are, but neither are very hard to locate either.
100%: 3-10 hours
Player
On top of doing missions, helping others, finding items and tracking animals, players should also work on improving Arthur/John themselves. The player improvement requirements are mostly simple -- all stats could theoretically be maxed by just playing the story, for example -- with a few exceptions.
The nine challenges all feature ten sub-challenges that progress in difficulty, and though some are as simple as picking a few plants, others can be hard to overcome. One particular sub-challenge requires players to win three hands of poker in a row, which can be very hard to do due to the game's difficulty settings, especially if a player is not experienced with card games. Finding treasure, robbing trains and hunting the legendary Giaguaro can take some time, but any player can reasonably achieve them with a little persistence.
100%: 5-10 hours
Miscellaneous
Inarguably the easiest of all the sections, the miscellaneous quests don't really pose any challenge. If a player hasn't completed them all naturally, even the most difficult requirement, killing all five legendary animals, is just a matter of quickly tracking them and unloading on them with Deadeye as their pelts cannot be damaged. Finishing these up could take anywhere from no time at all to just an extra hour or two.
100%: 1-3 hours
World Record
At the time of this article's writing, the Any% (no checkpoint skips) world record holder, according to speedrun.com, is Hess, who completed the story missions in 13 hours and 17 minutes. Coincidentally, Hess also owns the 100% completion world record at about 35 hours and 13m. Given how long-winded, difficult and random some of the quests and requirements can be, seeing such low times in comparison is incredibly impressive.
Final Play Time (100%): 104-168+ hours