Don't know exactly how it's set in terms of days, but after everyone from the tower is outside, Diego tried/tries to help Leo just enough to make the raft work. He then swims to shore on his own

He'll then be exploring buildings.

He'll find a lot of stuff in the general store, apparently. But his Umbrella Academy uniform (after years, I assume), which just makes things weirder...and he'll also find a bloodied photo of Vanya

which he'll keep, along with his platoon photo. And he'll be wearing the Academy uniform

He'll find some knives in the restaurant

He'll then find Town Hall and go in there to find information

I should make a log post for different places people can find him...