Depends on your commitment to gathering relatively scarce resources that were once plentiful back when this game was much more active. There is also a ton of story content buried in the questlines, and there are hundreds that provide actual lore.
Any less than that and you're going to grind yourself down to a nub with the tedium of the travel time (Wings), badly designed escort missions (CoP) and Midnight JST waits (ToAU). To see all of the major mission content I'd give myself about 3 months, starting from scratch and playing every day. Rhapsodies (the finale mission line) requires significant progress through all of the above to advance to the end, and on its own takes another week-ish to get through the soloable parts, and then you hit Reisenjima and need help for the rest of the missions like any other mortal. So maybe two weeks to get through the soloable parts, and however long it takes to get help for the fights that are more difficult to solo. Several missions are gated behind progressing through Coalition Quests, which consume resources that accrue at the rate of 3 per 24 hours. Absolute Virtue has earned a place on this list for time-it-takes-to-defeat alone. Lead Game Master for Final Fantasy XI, claimed that the Absolute Virtue battle takes about 18 hours. Seekers of Adoulin missions can take a while. According to an article from Destructoid back in 2008. There are a LOT of them and it's a ton of running around, moreso than Zilart. Wings of the Goddess Missions can be done in a weekish but it is a slog. It’s time to finish up Eureka in Final Fantasy XIV, as today marks the release of the fourth and final area, Hydratos.
#Final fantasy xi absolute virtue plus
Plus you're gated on finding equipment/crafting materials that can be scarce on low-pop realms (being in a big linkshell helps here). Treasures of Aht Urghan Missions are gated behind a lot of Midnight JST waits between sections, so that's about two weeks on its own. Once you're 99 with a leveled subjob you can get Rank 10, all the Zilart Missions and all the Chains of Promathia missions done in about a month of fairly casual play. Getting to 99 without an exp campaign up (one is about to end) will take a week-ish, depending on luck/help doing the limit break quests that let you get past 50/55/60/etc. Fortunately the game introduced two new currencies (Sparks and Accolates) that shortcut you to a workable set of gear at almost every level if you do the correct quests and keep your income of Sparks/Accolades steady. XI is all about your gear, whether or not you have an interest in endgame. Depends on how aggressively you push through the content and how efficient you are at gearing your character.