Sega and Atlus' latest sci-fi game 13 Sentinels: Aegis Rim defies convention. Not exactly an RPG, but also not really a visual novel, there's a lot of different elements at play that combines to make an intriguing and engaging story. In my review, I said that everyone with even a remote interest in this game should give it a shot, but how long does it take to beat?
Since your time is precious and you may not want to engage with a long story at the moment, I'll get right to the answer. 13 Sentinels: Aegis Rim is between 30-35 hours long. The core story is broken up between RTS gameplay segments and a less interactive story portion. The dialogue-heavy narrative sequences account for roughly 80% of the run time and can be cut down quite considerably if you just mash X a lot.
You'll rob yourself of the wonderful story, but that is one method of blitzing this game. Another would be to turn the difficulty on the combat sections down to Easy mode. I found Normal to be relatively breezy, but the story is the main draw here. I wouldn't blame anyone for putting the gameplay on Easy and getting back to the well-written story.
Once you complete the final mission, a series of bonus combat scenarios will open up. I'm not exactly sure how many there are, but the menu shows around 15-20 more battles. This could extend the gameplay another few hours, depending on how difficult they become. There's no reward for doing these, but it's a good way to test your skills after finishing the campaign.
There's also the mystery files you can unlock, which will contribute to the game's various trophies. Overall, the trophies are incredibly straightforward and you may even end up getting the Platinum without trying. By S ranking every mission and completing all optional objectives, you'll be basically 90% of the way there by the time you've hit the last mission.
So there are ways to extend what you get with 13 Sentinels: Aegis Rim. The main campaign isn't short, but I also wouldn't call it epic in length. This is a satisfyingly lengthy adventure that may run a bit long but doesn't overstay its welcome.