How is the peak at 2.4 so low?

Let's catalog them https://www.esp32.com/viewtopic.php?f=13&t=7669 https://www.esp32.com/viewtopic.php?f=13&t=7053 https://www.esp32.com/viewtopic.php?f=13&t=5461 https://www.esp32.com/viewtopic.php?f=13&t=7866 https://www.esp32.com/viewtopic.php?f=13&t=7499 https://github.com/espressif/esp-idf/issu...

Make your struct into a 64bit value which is supported by nvs. Hours and minutes don't need to be 32bit values.

Sounds fine as long as the risk of brick if power is lost during bootloader/partition writing is acceptable.

Websocket or Mqtt

No because when you call that in the app it is going to give you the version the app was compiled with and could be different from the version the bootloader was compiled with.

Needs at least 2 sectors so 8k but it would be nice if support for read-only single sector nvs was added

You could calculate a checksum/hash of the bootloader partition and compare it to known values or check for the version string at known addresses (which will change depending on the version) or append the version to the end of the bootloader binary. But no I don't think any function is provided to d...