Time taken to chill down 1 degree depends on few factors. Tank heat load, tank water vol etc. My resun 450 takes about 15min to chill down 1 degree and rest for about 45min. To see if u are using the right chiller, worse case is running time vs standby time is 1 : 1. Example if your chiller run for 2 hrs but rest for only 1 hr, then high chance your chiller is undersize or due for gas top up.
2000l/hr is for bigger hp like 1/4 or 1/2hp. Not sure where u read it, but online states cl280 pump required is 500l/hr