It would seem a tricky story to track from a structural standpoint with so many characters and their respective subplots — Jo, Amy, Meg, Beth — but if we look at the story with Jo as the Protagonist, here are some key plotline points:

Act One End: “Our Beth has taken a turn for the worst.” Jo boards the train to Concord. (21–24)

Midpoint: “Jo asks Laurie to stop Meg from falling in love, and Jo gives Laurie her ring.” (58–60)

Act Two End: “Jo wakes to find Beth gone, like in the past. Descends the stairs. Marmee breaks. Jo comforts her mother in pain over losing Beth.” (91)

The time jumps add all sorts of dramatic irony as well as complexity to the plot. You can read this in-depth interview with Greta Gerwig where she talks about the rationale for the past and present timelines.

For all its complexity in terms of plotting and multiple storylines, the story hangs together with this: Jo’s development and emergence as a writer. That’s the single cleanest throughline of all the subplots.