Shin Megami Tensei timespan headcanons
Shin Megami Tensei I: Several years, not counting the timeskip. Travel and survival is going to eat up a lot of time, and you see each of the factions rise, fall, and grow as you move around. The first section in Tokyo seems like it should have been at least a month, since the Heroine's Resistance movement needs time to gather enough steam to be a known threat
Shin Megami Tensei II: Been a while, so I can't remember details. Also seems like a few years.
Shin Megami Tensei III Nocturne: No more than a year. Don't have any hard evidence for this, but it's enough time for the students to develop their own perspectives on the world, without the years weighing on them.
Shin Megami Tensei IV: This one has a canon guideline. Basically, the artbook says that Gaston was nine years old when Navarre was eighteen. Gaston is eighteen now, and it's a 1:75 time ratio between Tokyo and Mikado, so we know that around 43 days passed between Flynn's Gauntlet Rite and the endgame. But there's still a lot of room for fudging, especially since Flynn spent time in Mikado and parallel timelines. I also think that the Prentices had at least some rudimentary sword training before going into Naraku.
Shin Megami Tensei IV Apocalypse: The only game that shows each day, and there's ten of them. But since it's from the new moon to the full, I say it was fifteen days, and Nanashi did sidequests between plot days. The last dungeon could take longer than a day; there's no more time pressure, and someone in the Ring of Gaea on Anarchy says the Cosmic Egg was there for a few days.
Shin Megami Tensei V: Several months. The first act is an eventful afternoon, and the second act feels like a hectic week. The third and fouth acts, where it's all-out war, could take a month apiece, maybe more. And there's room for offscreen training and side missions between acts; I think there were at least a few days between the first and second acts, just so that Bethel didn't greenlight Ichiro dropping into Da'at the day after he received the Demon Summoning Program.
