I think, there’s a opportunity for improved behaviour on the tibber binding side.
following this thread:
I set the change to 25mins. My thinking was to eliminate the change every minute, which was logged excessively! 
This led to the binding “rotating” also the hourly price every 25mins. So it was randomly ok for a time, but could be as much off as 25mins. I’ll try to file an improvement issue for it on github.
for the time being, I changed it to 60mins exactly on the hour, so until a restart of openHAB outside of “on the hour” I’m safe.