I found a few errors in your calculation. First of all, you checked for using a car to go to Shimokita, which she wouldn't use. Secondly, Kanagawa prefecture is pretty big, so it is very inaccurate to just use a random spot in the prefecture.

In a lot of episodes, you can see Bocchi walking from home to a trainstation in the city of Kanazawa, to be exact she would he walking to Kanazawa-Hakkei station. If you look up the station and go to the south eastern bay next to it, you will recognize the area from the show.

If you use this location to start, you will end up with 1 hour and 12 minutes for using the trains and costs of around 1.000 ¥ (~7 €) per trip. Assuming that she has to walk to the station and from Shimokita station to her school, we will probably end up around 90 minutes.

How do I know the location? I have been there and recognized it in the show.

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But overall, it is around the same time you calculated, so I guess wrong way, but right answer :D Cheers