I don't know that it's unethical, but I certainly wouldn't feel right about just letting their clock run down.  Me, personally, I'd let them know no matter what the time control.

I just wouldn't feel right about winning in that manner.

Playing out a losing position when I have a significant time advantage on the other hand..., that's part of the game.

NO it was never "normal" as in mandatory to have to alert your opponent to check or attacking his/her Queen. I never announce check in tnmt games. Nor do you have to tell your opponent to hit their clock - I do in casual games but not in tnmt games - although I might in some cases depending on my mood that day.

Chess for Tigers ;)

I'd let the clock run for about 1-2 min, then remind them.

Let it run to 1-2 min, then suddenly 'notice' it and kindly remind them out of the goodness of your heart.