JSON node palette to process MQTT payload. In this case usemsg.payload string and then split the payload. Please refer https://discourse.nodered.org/t/how-to-split-mqtt-tag-values/10794/3. As @techielew mentioned, we're preparing for TODAY's Engineering Hour. I'll write you detail response late evening.
JSONmsg.payloadmsg.payload : Object
{ sunrise: 1713645121, sunset: 1713684720 }