@rigpapa: your assumption is right. I went through your documentation already (very well done!) but missed the links to LuaXP.
Now I succeeded. I also used another string function sub(s,i,j).
For other users: I use a Reactor Sensor to retrieve data from a weather API (only Dutch “Buienradar”) for predicted rainshowers. It gives a warning notification (in seconds before the rainshower starts), the predicted rainintensity and also the starttime and stoptime of the rainshower. These times are in Unix timestamp and I converted these in 24h readable times.
I use the sub function to skip the seconds (because they are always “00”).
StartRain = tonumber(getstate( 1105, “urn:brutgrink-com:serviceId:dutchRainAlarm”, “StartRain” )) gives 1627241100
StarttijdRegen = sub((strftime("%X",StartRain)),1,5) gives “21:25”
Within an hour I know if the prediction was correct