The cake in question (mostly I just want a chance for everyone to admire my beautiful cakes)
So, I thought it was extremely commonly understood etiquette that if you are at a birthday party and there is a cake, that it is a Birthday Cake and should not be cut into until Candles Are Lit and Happy Birthday Is Sung, and yet…
So here’s a hot tip that is good most times- don’t be the first to cut into something at a party unless you are told that it is okay.
uncommon-courtesy.com 
This might be the first time I’ve disagreed with you! I think, if there’s a food item at a party that’s intended to be off-limits until a particular time, the host has the obligation to let people know that, or to put it somewhere separate from the food you’re allowed to eat. If I wanted to display your beautiful cake — which really is beautiful, by the way — for a while before actually serving it, I’d put it on a separate table from any other food, possibly with decorative stuff around it to make it more obviously a display rather than a buffet, and probably even then I’d feel the need to tell everyone “We’ll be serving the cake at 6!”