The heat mat should be put on when you turn the beardie's light and heater off of an evening, then turn it off when you put the light and heater back on in the morning. I hand feed my young beardie, so there is no chance of her eating sand. But all animals are different, if yours will not hand feed then it would be best to put kitchen roll down until he/she gets a bit bigger. Feed him/her with the dusted locust two/three days a week.
I hope this helps.