What is the rule for eating after midnight?

So my mother raised my sister and I telling us we cannot eat after midnight, unless it’s during a special occasion (like a celebration or family gathering or something), when we get our Holy Communion it is on Sunday morning, having fasted from midnight until we receive the communion, standard practice of no food or water. I just got into an argument with my sister as she very strictly seems to mention this rule a lot (until it is up to her inconvenience), in this case I wanted one of the cookies I bought for myself after having had a long day and didn’t particularly feel like sharing since I’d made her a hot chocolate as per her request a few hours earlier, when she realised I wasn’t sharing she checked the time and told me off, threatening to wake up our mother for silly banter when she has to wake up early for work and really needs the sleep.

Now, I understand completely fasting after midnight prior to Communion, but does this go for all days of the week? Not referring to the dietary change throughout the week, but purely about the timing. My mother learnt a lot from those before her so she herself isn’t unsure of the variation, but in our language the word used to describe a sin and something that is not good for you, or something that is superstitiously considered bad luck is one and the same. Is the ‘no food after midnight on regular days’ just another olden myth and superstition in my family, or is this a true aspect of our religion?

I apologise for the long paragraph but it’s a question I’ve had in my mind for years and finally decided would be a good time to discuss.