1a. These slurps can be as long as your lung capacity and/or ability to circular breathe can make them. It is the number, not the length of time slurping, that is key here.
2. If someone asks for you to pass a dish of something at a meal, and you want that thing as well, you may call out, "Shortstop!" and take some for yourself as it passes.
2a. It is rude to shortstop something if there's only one person's worth left.
2b. Negotiations about splitting the last piece of whatever are permissible if handled without acrimony.
3. Towards the end of a holiday meal, the appropriate comment is, "Well, I wonder what the poor folks are doing." If this comment has not been made, preferably by an elder, do not ask to be excused; the meal is not yet over.