If you look online you will find multiple sources suggesting that the newest addition to the Kingdom Hearts franchise will have campaign play lasting about 40-50 hours. Not including the additional contend that will boost that number up to a whopping 80 hours of gameplay. Pay no attention to those rumors however. Square Enix hasn't even settled on the final length of the sequel as of yet and I am sure they will let us know when it is completed.
If you check out the website Geek.com, you will see a report that someone has confirmed those playtime estimates had been confirmed for Kingdom Hearts 3. Many other places used this report as confirmation as the official length of the game as well. Obviously if those numbers turn out to be accurate this will be the longest campaign in the Kingdom Hearts franchise to date.
If you were to check Geek.com now you will see that the original estimate is not at all accurate. They have since then updated to add in a note that Square Enix representatives explained the company has yet to finalize the exact length of KH3, given the remaining months of development.
Is it possible for KH3 to even be that long? Yes! If interviews before the franchise director Tetsuya Nomura explained they are working to make the worlds in Kingdom Hearts 3 more expansive than in the past. Just also keep in mind that the "Officially" announced game lengths are just that, estimations. Even when a game length has been announced, it really comes down to each individual player on how long it will last.
Given the possibility for an even longer than normal Kingdom Hearts game is super excited for fans of the franchise such as myself. There will be a lot of narrative tied into the storyline in this newest addition. Though Nomura has been very quiet about whether KH3 will be the finale of Sora's story.
The much anticipated Kingdom Hearts 3 will be releasing for the PS4 and Xbox One on Jan. 29th, 2019. Happy Gaming!!