Hmm looking further into it specifically from this topic MQTT Sensor : how to define last_reset_value_template - #20 by iSteeb
I’ve updated my config and home assistant likes it but I can’t confirm until tomorrow when I have daylight. [EDIT: it works 
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The other thing I think is if sbfspot itself would publish the last reset time via MQTT but I’d have to look into that aspect further.