GxEPD2 - Detailed analysis of fast partial update speed of 1.54 Waveshare

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A simple look at the driver header file GxEPD2_150_BN.h confirms your times:

    static const uint16_t power_on_time = 100; // ms, e.g. 94000us
    static const uint16_t power_off_time = 150; // ms, e.g. 140000us
    static const uint16_t full_refresh_time = 4000; // ms, e.g. 3825000us
    static const uint16_t partial_refresh_time = 800; // ms, e.g. 736000us