Thanks Lars for posting the graphs. I would want to see the raw data and see the specifics of how the data was captured. With HRV measurements you want precision to the microsecond.
There are many factors that will improve your overall analysis when using HRV. (1) To be able to determine your state of recovery you would want to be performing a min 3 - 5 minute session, daily, each morning at approximately the same time and in the same position. As with most biometrics they are dynamic and fluid. They will be changing through out the day depending on a multitude of factors so test at the same time each day. (2)The measurement time needs to be long enough. You can get a good enough rMSSD read in 3 minutes but in the frequency domain (LF HF) it needs a 5 minute reading. It uses a 5 minute moving window of data. It takes 5 minutes for the data to settle especially in the frequency domain. (3) The signal quality from the BLE device is important. Poor contact with the device (contact pads) can cause poor quality data. The filtering algorithms are important for removing electrical artifacts and ectopic beats from the data. Even if advanced filtering is used, too much bad data can cause a false high HRV result. (4) There are 32 different HRV metrics that can be derived from the RR data in the time domain, frequency domain and non-linear. Each metric gives different a different insight. When the phrase HRV is used it is important to be specific as to which metric. They are all HRV.
With all of that being said, maybe an average HR metric, daily (make sure it is measured at the same time of day) is sufficient for what you are trying to discover. Average HR is an excellent metric and frequently undervalued. It’s easy to capture and PPG devices are very good since it is an average.