I never make custard on the fly, always make it earlier, cover the jug with cling film and reheat it by standing the jug in a pan of warm water, which has always worked well for me. However, I have never (to my recollection) made custard the day before. I don't know why a few hours in the fridge and reheated should be any different to 24+hrs, but I wondered if anyone else habitually does this?