Problem with IFLO Digistat RF2 (Wireless System)

I am unable to operate my Thermostat properly. I have put it on the Timer setting and set it to come on at 18C at 5:20am and then go off at 23C at 10:00am. It is then set to come back on at 18C at 16:00 anf go off at 23C at 22:00. With the set it does not come on at the desired time and may event come on out of the set time periods.!! What am I doing wrong?

Many thanks for your time!