Okay, that’s a blog by some random guy… why are you looking there instead of at the source? The Goethe institute has word lists published for A1, A2, and B1:
Starting at B2, you’re pretty much expected to understand unknown words from the context and/or by using a monolingual dictionary, so forget about…
…and use the official Duden instead: Wörterbuch der deutschen Sprache ✒️ Duden Online
Basically that and do twice as much work every day to get it down to three months. Alternatively, you could read what I wrote here…
Make sure you cross-reference the Frequency dictionary with the B1 list in the above pdf as you work through the frequency dictionary.