what does the advance button do on BPS242RF?

after a sleeples night where the radiators were on full blast at 2.30am despite me following the "instructions" I think I have it sussed. A1 & A2 times are set; A3 & A4 times are set. Comfort (sun symbol heat temp set at 20C) setback (moon symbol cool night set at 10C). Boiler should not fire up outside these times?! But what is the 'advance' button for, and by sliding to standby does it switch the thing off!! Any advice would be immensley grateful!